A 421 email error is typically a temporary routing issue on the receiving mail server’s end. These should usually be resolved automatically, and you should receive a final bounce-back message if the message completely fails.
You usually would not receive a bounce-back message for this type of error. If your message is going to be delayed more than 24 hours, then sometimes a “delivery has been delayed” soft bounce will be returned to you, to let you know that the delivery has yet to complete succesfully.
Common variations of the 421 email error
- 421 4.2.1 : (DYN:T1) https://postmaster.info.aol.com/errors/421dynt1.html
- 421 4.3.1 Out of disk space for temp file
- 421 4.3.2 All server ports are busy
- 421 4.3.2 All server ports are busy
- 421 4.4.2 mx.aol.com Error: timeout exceeded
- 421 #4.4.5 Too many connections from your host.
- 421 #4.4.5 Too many connections to this host.
- 421 4.7.0 mx.aol.com Error: too many errors
- 421 4.7.1 : (DYN:T1) https://postmaster.info.aol.com/errors/421dynt1.html
- 421 4.7.1 POL-T2 https://postmaster.facebook.com/response_codes?ip=74.124.194.252#pol-t Connection refused
- 421 4.7.1 POL-T2 https://postmaster.facebook.com/response_codes?ip=74.124.194.252#pol-t Connection refused
- 421 Downstream server error
- 421 Fork failed
- 421 Greylisting enabled, please try later.
- 421 LDAP verification agent temporarily unavailable: Connection failed
- 421 mail.RemoteDomain.com out of connection slots
- 421 mx.aol.com Service unavailable – try again later
- 421
- 421 Server busy, try again later – psmtp
- 421 service temporarily unavailable
- 421 Temporary error (#4.3.0)
- 421 Too many concurrent SMTP connections; please try again later.
- 421 Unexpected failure, please try later
Resolving a 421 email error
Because errors in the 421 series don’t bounceback right away they would be considered a soft bounce. To better understand soft and hard bounces, and general email bounceback errors you can read why does email bounce, bounceback, or error?
Seeing a large amount of 421 email errors in your server’s mail logs could be an indication that a lot of your mail users are having difficulties getting their e-mails delivered out successfully on the first attempt.
Enjoyed reading the article above , really explains everything in detail,the article is very interesting and effective.Thank you and good luck for the upcoming articles
My office keeps getting mail delivery failed emails being sent. They started months ago with just aol email addresses. We would receive the following error messages:
SMTP error from remote mail server after end of data:
521 5.2.1 : (CON:B1)
Now we are receiving errors for other email accounts outside of aol that say:
Delay reason: SMTP error from remote mail server after initial connection:
421 Deferred
Please help!
This looks most likely like a graylisting. Graylisting is a method implemented by some email servers to protect against spam. When you send an email to a person that uses a gray listing spam filter, that mail will be checked against an approved list. If the address is not on the approved list then the message will be sent back with a “try again later” message. This happens at the SMTP layer and is transparent to the end user therefore, the person you are trying to send to will not know the message failed. The receiving system will then wait to see if you try and resend the message.
Ensure you have DMARC records setup, as well as SPF Records and DKIM. This will give your email the best chance at successful delivery.
If the emails finally fail/bounce, they should provide a more detailed error message.
Thank you,
John-Paul
Hi guys, I got this error when sending out to our email list.
421 Too many concurrent SMTP connections
Is there a way to correct this error?
It depends. If you’re on shared hosting and sent out a mass email from one email username it’s possible that the resources were expended. I’d suggest using a program like phpList. Or, even easier, a third-party email marketing service like MailChimp/
hello,
Need anyone to help.
Your message has encountered delivery problems to the following recipient(s):
[email protected]
(Was addressed to [email protected]) Delivery failed after 1 attempts within 0 minutes
550 Too busy for PTRless hosts
No recipients were successfully delivered to.
Hello Chola,
You will need to request a PTR from our live technical support team. You can do this by submitting a verified support ticket. Make sure to include your verification info and the domain you need the PTR for.
If you have any further questions or comments, please let us know.
Regards,
Arnel C.
Please help – I am trying to run a business and have had this problem for four days. Both my btinternet account and my work based (gmail) account are affected. My husbands similar accounts are not. All emails are soft bouncing back over a few days.
What practically do I need to do? I am stuck without email.
Jenny, I’m sorry to hear that you’re having this issue. I would recommend contacting your email host for more direct, specific assistance with the issues you are having.
An unknown error has occurred.
Subject ‘Test 4test4’
Server Error: 421
Server Response: 421 service not available (configuration error, try again later)
Server: ‘mail.danaeng.com’
Windows Live Mail Error ID: 0x800CCC67
Protocol: SMTP
Port: 25
Secure(SSL): No
Dear Sirs,
I have still the avove error, I wrok with windows live Email
please help how can I resolve this problem
Since this is a temporary error, it may be delivered once the issue is resolved. I recommend checking your mail logs for additional errors, or record of your transmissions.
Thank you,
John-Paul
Hi for respond!
Well, i try again and i have the same issue:
Identity: VM-EXCHANGE\205953\21603685499442
Subject: Test 2
Internet Message ID: <a07c4544f276467e82f484ef8f119376@VM-EXCHANGE.*****mty.local>
From Address: Siddhartha.Zuniga@*****.com
Status: Ready
Size (KB): 8
Message Source Name: SMTP:Default VM-EXCHANGE
Source IP: 172.16.9.19
SCL: -1
Date Received: 6/10/2016 9:53:24 AM
Expiration Time: 6/12/2016 9:53:24 AM
Last Error: 421 dalifep04.*****.net connection refused from [201.151.62.115]
Queue ID: VM-EXCHANGE\205953
Recipients: [email protected];2;2;[{LRT=};{LED=421 dalifep04.*****.net connection refused from [201.151.62.115]};{FQDN=};{IP=}];0;CN=Correo a Internet 2013,CN=Connections,CN=Exchange Routing Group (DWBGZMFD01QNBJR),CN=Routing Groups,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=*****,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=*****mty,DC=local;0
Identity: VM-EXCHANGE\205953\21603685499442
Subject: Test 2
Internet Message ID: <a07c4544f276467e82f484ef8f119376@VM-EXCHANGE.*****mty.local>
From Address: Siddhartha.Zuniga@*****.com
Status: Ready
Size (KB): 8
Message Source Name: SMTP:Default VM-EXCHANGE
Source IP: 172.16.9.19
SCL: -1
Date Received: 6/10/2016 9:53:24 AM
Expiration Time: 6/12/2016 9:53:24 AM
Last Error: 421 dalifep04.*****.net connection refused from [201.151.62.115]
Queue ID: VM-EXCHANGE\205953
Recipients: [email protected];2;2;[{LRT=};{LED=421 dalifep04.*****.net connection refused from [201.151.62.115]};{FQDN=};{IP=}];0;CN=Correo a Internet 2013,CN=Connections,CN=Exchange Routing Group (DWBGZMFD01QNBJR),CN=Routing Groups,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=*****,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=*****mty,DC=local;0
and its in only this domain :/
Hello Siddartha,
Exchange 2013 is an email server that uses Windows Servers. We are a linux-based hosting service and we do not support Exchange 2013. You may want to consult with Microsoft for further assistance if your error persists. You will find more support for Exchange here.
If you have any further questions, please let us know.
Kindest regards,
Arnel C.
Hi! i got this error with only one domain. I have Exchange 2013.
Remote Server at mail.suddenlinkmail.com (208.180.40.132) returned ‘451 4.4.0 Primary target IP address responded with: “421 dalifep05.suddenlink.net connection refused from [myEmailServerIP].” Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was 208.180.40.132:25′
Hello Siddhartha,
Thank you for contacting us. Since this seems to be an issue on the recipient server, I recommend resending the email at a later time.
When/if the email completely fails, it should provide a more detailed bounced message.
Thank you,
John-Paul
421 .x.x.x is a temporary rate limiting by ISP because your sending IP does not have adequate or good reputation.
You should first build reputation on those IP’s and then start sending faster in time.
I advise sending your message again to see if the issue has corrected itself. These are typically temporary errors.
Hi! How about error 421 4.3.0: Cannot write? I’ve been searching for this error but unable to find any answer. Please assist.
your email message was unable to be sent because your mail server rejected the message: 421 4.3.0 collect: Cannot write .dfu37H6eot023017 (sm_io_flush | |sm_io_error, uid=0, gid=51): Input/output error
Thanks in advance!
Hello Kim,
It looks like there are several possibilities. However, I did find a post explaining the main possibility: Sendmail not working: permissions issue. Check out the post and see if it doesn’t help you resolve the error.
If you have any further questions or comments, please let us know.
Regards,
Arnel C.
when i sent e-statement to cardmember I’m getting this error. what should I do to prevent recurrence.
421 4.4.5 System rule action set to defer or all IP Addresses have reached their throttle limits for this time period
I have two identical VPSs. Identical diagnostic message are sent daily from both. Error messages keep showing up in the mailq: D6D3980758 1896 Tue Jan 19 06:01:27 [email protected] (host mx.suddenlink.net[208.180.40.132] said: 421 dalifep01.suddenlink.net connection refused from [my.se.rv.er] (in reply to end of DATA command)) [email protected] Suddenlink tells me to check my server. 208.180.40.132 has ACCEPT before a DROP 208.0.0.0/8 record. Both servers are setup this way. Does this look like a suddenlink problem to you? Their email system went down once this month but is supposed to be fixed. Thanks.
The IP listed in that error is blacklisted and refusing connections. The hostname is mail2.infospacesg.com.
Likewise, as in the above comment, the IP address listed is blacklisted with an anti-spam service and refusing connections. It’s possible this is temporary and may resolve itself soon.
Can any help me? I can’t send my email out. t=The error message that bounce back is:
Reason: Mail Server for kodoinc.com could not accept your email at this
time. MailEnable will keep trying to deliver this message and will notify
you of any progress.
The remote mail server returned the error:
421 dalifep05.suddenlink.net connection refused from [103.31.228.142]
We have recieved NDR while sending mail to aol.com domains.
Error Code:Queued: 152.163.0.99, 442 Bad Connection. (Timed out)
Hello Saravanan,
In order for us to troubleshoot this issue we would need more information. We need the fool bounce-back message as well the email address involved in the bounce. Please provide us with more info and we can investigate. If you want to handle it privately, then please submit a verified support ticket or call/chat with our live technical support team.
If you have any further questions or comments, please let us know.
Regards,
Arnel C.
Please I need help so badly and urgently.
Anyone to help, I will be very grateful.
Each time i try to send an email, I get an error message
[SMTP Error: [421] Unexpected failure, please try later]
I can’t even receive emails and besides orders place by our customers can not be delivered to our email address because of this error.
Can anyone help me, I will be very grateful.
Thanks in advance and looking forward to your humble explanation/solution.
Hello Edwin,
Email bounce issues will require a conversation involving account specific and personal information. If you are one of our customers, you will want to contact our Live Support team so they can work with you, check server logs, etc.
Kindest Regards,
Scott M
Thank you for your reply.
Hi,
I get this error message from one address. I have tried sending mail twice with one week in between.
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
@HANMAIL.NET
host mx4.hanmail.net [180.70.93.98]
SMTP error from remote mail server after initial connection:
421 4.4.5 CCRT 79.172.204.140: Connection refused. Server is busy(RT):
retry timeout exceeded
Hello Pallos,
I’m sorry to hear that you’re having problems with your email being delivered. When I looked, it appears that you’re not hosted with us (at least per the information that I could see in your post). The message is not showing the entire email address, so I’m not sure if you took it out, if the address was not correct. If the error is occurring between you and another host, you would need to contact the email administrator of the destination server to see why your message is not being delivered – since you’re not getting a clear reason why. They may have your domain blocked. It does not appear that you are hosted with us, but if you are, we would need more information about your account in order to determine the reason for the delivery failure.
I hope this helps to answer your question, please let us know if you require any further assistance.
Regards,
Arnel C.
Hello Edens,
Yes, I’m getting this error to a certain email server only.
Hello Shuvro,
Thank you for contacting us. Since it is just a delay at this point, I recommend allowing additional time for the delivery to complete. You should get a returned/bounced email if it fails to deliver.
If it fails, I recommend reading our guide on What to do if an email is returned.
If your problems to persist, review the mail logs on the server that is failing. You may have to contact the recipient to complete this.
Thank you,
John-Paul
This is a weird one. I get “421 esmtp protocol deviation”. This only happen around 1% of the time.
Hello Martin,
As per the definition above, the 421 message you’re seeing is the same error definition as above. Typically, it means that there’s an interruption in connecting to your email server. If you want more information than what is provided above, then check out : smpt error codes.
I hope that helps to answer your question! If you require further assistance, please let us know!
Regards,
Arnel C.
Hi thanks for the offer of help. This is the main part of the error message. After this there is a string of information about the return path and thread index as well. Do you need to see this (with addresses removed). Sue
Hi. This is the qmail-send program at emailserver1.aplushosting.com.
I’m afraid I wasn’t able to deliver your message to the following addresses.
This is a permanent error; I’ve given up. Sorry it didn’t work out.
<[email protected]>:
216.82.251.230 does not like recipient.
Remote host said: 421 Service Temporarily Unavailable
Giving up on 216.82.251.230.
I’m not going to try again; this message has been in the queue too long.
— Below this line is a copy of the message.
Hello Sue,
Thank you for contacting us. This email is being delivered, but the recipient server is denying it due to the following reason:
421 Service Temporarily Unavailable Giving up on 216.82.251.230
It is a possible spam rule, or blacklisting that is denying the email. Unfortunately, the recipient will have to whitelist you, or review their mail logs for more information.
Thank you,
John-Paul
Hi
I wonder if you can help. I get the following error message to only one address (although it occurs with the different names in the address ie [email protected] and [email protected]). But it does not happen consistenlty – every now and then one gets through.
Any ideas?
216.82.251.230 does not like recipient.
Remote host said: 421 Service Temporarily Unavailable
Giving up on 216.82.251.230.
I’m not going to try again; this message has been in the queue too long.
Hello Sue,
Can you post the full email header (while modifying the email address) so we may try to help you figure out the issue at hand.
Best Regards,
TJ Edens
Hello,
I’m getting following error message:
“Delay reason: SMTP error from remote mail server after end of data:
421 Read data from client error“
What does it means?
Thanks–
Hello Shuvro,
This can be caused for many reasons. Does this happen every time you try to send an email? Does this happen on many recipients or just certain ones?
Best Regards,
TJ Edens
Inmotionhosting (IMH) is hosting our mail server. We are getting occasional AOL soft bounces, as
Delay reason: SMTP error from remote mail server after end of data:
host mailin-04.mx.aol.com [64.12.88.132]: 421 4.2.1
(DYN:T1) https://postmaster.info.aol.com/errors/421dynt1.html
which AOL claims is due to
My questions:
1. Since AOL is bouncing based on our IP address, is this a function of IMH’s server’s IP, or our specific account? I would think the former.
2. If the former, then what might IMH do to alleviate this problem?
3. If the latter, what might we have done to cause this, and how might we alleviate it? To the best of my knowledge, we do not email in bulk.
4. Additionally, occasional emails from AOL to us go missing, but I have not yet traced that problem.
Thank you.
Greg F.
Hello Greg,
I will try to answer you questions as best I can:
1. Since AOL is bouncing based on our IP address, is this a function of IMH’s server’s IP, or our specific account? I would think the former.
– It is likely the former, particularly if you are on a shared server. If you are on a VPS or Dedicated, then it would be both.
2. If the former, then what might IMH do to alleviate this problem?
– You can email the bounces to our Live Support department and they will check out the situation. If they can repeat it from the server, then it would go to our Systems team to be handled.
3. If the latter, what might we have done to cause this, and how might we alleviate it? To the best of my knowledge, we do not email in bulk.
– If it is the latter, it would have to do with their own set of rules, but we would not have any way to identify them. You would need to reach out to AOL and ask them which rules your emails are violating. But again, the odds are with the server IP being the issue.
4. Additionally, occasional emails from AOL to us go missing, but I have not yet traced that problem.
– If you have incomgin emails missing, you can contact our Live Support and provide the email address and approximate time the email was sent to you. They can then check the server logs to see if any contact was made from AOL side and if so, see how our server dealt with the email.
Kindest Regards,
Scott M
We just received notice that people are getting the bounce back with this:
Failed to connect to xx.xx.xxx.xxx Server temporarily not accepting mail at Greeting – 421 4.3.2 Service not available, closing transmission channelServer refused mail at MAIL FROM – 530 5.7.1 Client was not authenticated
I have never seen this before so not sure where to look for the problem. Any help or guideance would be appreciated. Thanks.
Hello Jeremy,
This error is stating that the client was not authenticated, this means that you need to make sure you are passing your email accounts password for outgoing mail authentication. Depending on the client you are using it can be done in a few different areas.
Best Regards,
TJ Edens
Looks like some changes happened since the last time we talked. There are some new features and yes, there error issue is gone. Thanks for the help.
It happens with every email I send. Every person that accesses their email via a computer or laptop, has this issue. (in our company that is). As far as timing out, the instant I click send, the error pops up, literally 1 second later I can hit send again and it goes through. As far as the outgoing client settings, no one has made any chages to anything nor would anyone attempt to do so. Additionally, I use my laptop on the road using a wireless connection complete separate and different than any connection at the office and I still have the same issue. It is also a different OS than the computers at work. It seems the only common denominator, is the mail server.
The problem on a whole isnt that serious, but it does sometimes slowly send the email after the error. Sometimes taking over a minute to send a plain text email.
Hello Jason,
Okay, if you’re getting the problem across the board with everything connecting to the account, then it’s definitely an issue with the mail server. I was able to test here and duplicate the error as well. One thing that may have been causing it is the list maintained for handling remote and local domains for email. Yours is set to local domain – meaning that email is handled by our server. The suggestion given to me by one of our senior techs was to remove your domain temporarily (very briefly), and then re-add it. When I did this, I logged off of my webmail test account, then attempted to re-duplicate the error by logging in and re-sending a test email. The error did not reappear at this point.
Try testing it on your end now. Please let us know if you continue to see any errors. Hopefully, this issue has been resolved.
Kindest regards,
Arnel C.
I use multiple devices and have been using the same mail settings for years. I use an Imac at the office and an HP laptop in the field. Also, my CFO and receivables manager are having the same problems. I havent noticed issues send from my phone or tablets only desktops and laptops.
As far as bounceback, I havent received any as of yet, but like I said, it usually goes through a second later.
“And what specific settings are you using?” I dont know what you mean specifically, but nothing has changed in the passed week except the errors.
Ill look through the reference guide as well. Its just weird that after not having anything like this ever, then have it happening to multiple people on different accounts, on different computers.
Hello Jason,
I can understand the concern and the confusion on the issue. The problem here is that your device/computer is trying to make the connection to the server. When it does this, anything that causes a delay or interruption in that attempt to deliver could be causing the error. Since we do not have control of your network (only the servers), it’s difficult for us to determine what factor could be affecting only the computers of your system. It could be an internal network issue, an ISP (internet service provider) issue, or maybe you are making a connection, but it is slow to synchronize causing a timeout. The settings I’m referring to are the outbound email client settings that you are using to connect to the server. So, if it’s a computer, does the problem happen consistently from specific accounts? That information would be invaluable for testing on our end, so that we can determine if the problem does exist on the email server.
We appreciate your patience as we work toward resolving this issue.
Regards,
Arnel C.
Been getting this for the last week on mulitple accounts here. When you first attempt to send an email to a wide varity of servers this message will pop up every time. Most times you can just click send again a second later and it will go through but sometimes it will lock you out for almost a full minute. Any idea what caused this and/or how to fix it.
SMTP Error (421): Connection to server failed.
Hello Jason,
Sorry to hear you’re having problems with the server connection when you’re trying send an email. We need a little more information though. When I checked the server, I found no error messages or problems with connection. I also checked on the server history, and it appear to be okay. There are a large variety of possible factors for this kind of problem, so we need more info in order to help pinpoint the problem. Are you using a computer or device to connect to email? And what specific settings are you using? Do you get any bounceback messages? I’m seeing no error messages in the logs on this end.
Also, please reference Problem with sending email for further help in troubleshooting the issue.
If you can please provide us more information, then we can get back to you after investigating the issue in more depth..
Kindest regards,
Arnel C.
Hi JrffMa,
Thanks, sure…will try to do that…
Hi,
I am getting an error when I am trying to send emails to some domains(ocscmb.com, falco.lk).
This is the mail system at host relay.mailchannels.net.
I’m sorry to have to inform you that your message could not be delivered to one or more recipients. It’s attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
<[email protected]>: host mx07.register.com[205.178.149.7] refused to
talk to me: 421 Downstream server error
The error I am getting is in bold above. Please explain me the reason and a solution for this.
Thank you very much.
It appears that the remote mail server that you are sending to is closing the connection. Unfortunately, as their mail server is outside of our network, we do not have the specific reasoning as to why. For this, I recommend speaking with the individual that you are attempting to send to by other means to identify what on their server may be causing the issue.
I am getting the error accompanied by an Unexpected log failure
Can anyone please help me>
Could you provide us with the exact error that you are getting?
different email addresses. similar messages – as I work for a charity and I send membership packs by email. I have been using outlook 2007 to do this for years and only now is it a problem
How big is the mailing list? Are you sending them all at once? A specific service provider is most likely seeing a lot of messages coming in to their users and blocking based on that to prevent spam.
this has been happening for about a week now. I send lots of mail and have done for years but I am only getting these error messages for the past week.
the worst pop up box is the grey one that says do you want to save this password in the list, it pops up every two seconds, it is so annoying. i dont know what to do about it.
I am not at all technical and I dont have anyone that can help me 🙁
Are you sending multiple messages in succession to the same email address or to a bulk mailing list?
I am getting 421 error – too many messages? what does that mean. also I am getting a grey pop up box that says do you want to save this password in the list, everytime I send sonmeone an email, what does that mean?
I am able to send and receive emails OK, just these annoying two pop up boxes that wont go away. please help
This error is typically from the receiving server so it should not be a result of your account. It seems that the receiving server may be getting more mail than it is set to expect, so it is giving the “too many messages” message. You may want to try resending the email again at a later time to see if it will accept it.
Kindest Regards,
Scott M
I keep getting “too many simultaneous connections” for my AOL account. I have a multitude of phones, tablets, and computers that have my AOL account attached. Is there a limit to how many “connections” I can have? If so< what is my next step? If not. how to I remedy this?
Kady
Hello Kady, and thanks for your comment.
Are you getting this error just when trying to send email to an AOL email account? This guide itself is on 421 errors, and you would typically see it in a bounce-back message after a message you sent to a AOL user failed to send. In this case you would want to try to send the message again at a later time as the AOL server could be temporarily overloaded.
If you are just getting this error in your mail client, and you are using your AOL account in multiple devices at once, you might be having an issue with IMAP usage on their server.
You might need to stagger the times your different devices check your mail. For instance, have your phone check every 5 minutes, tablets every 7 minutes, first computer every 9 minutes, and so on. You might also want to reduce the total number of messages stored in your main Inbox folder, and archive away messages you don’t need to access often. Some email clients will tie up IMAP connections by trying to download lots of old message headers from the server for a message that’s older than 30 days and you might not be reading anyways.
Hope that helps, please let us know if you still have any questions at all!
– Jacob