Hello,
Thank you for your question about restoring email service. We are happy to help, but will need some additional information. What is the exact error they are getting?
Are they getting a Mailbox Quota Exceeded error? That guides explains how to increase the Mailbox size if it is necessary.
Are you getting a Domain has exceeded the max emails per hour error? That article explains the options in this case.
If these are not helpful, please provide more details, so we can help narrow down the cause. If you have any further questions, feel free to post them below.
Thank you,
John-Paul