4.7.500 Server busy

4.7.500 Server busy

Recently, most of the letters sent via imap are rejected by microsoft servers and arrive with the following text:

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.

some@email.com, ERROR CODE :451 - 4.7.500 Server busy. Please try again later from [31.186.226.227]. (S77719) [DM6NAM12FT022.eop-nam12.prod.protection.outlook.com 2023-06-01T17:48:19.869Z 08DB6279EB7055FC]



Reporting-MTA: dns; mx.zohomail.eu
Arrival-Date: Thu, 1 Jun 2023 16:52:49 +0000

Original-Recipient: rfc822; some@email.com
Final-Recipient: rfc822; some@email.com
Status: 451
Action: failed
Last-Attempt-Date: 1 Jun 2023 17:48:19 GMT
Diagnostic-Code: 4.7.500 Server busy. Please try again later from [31.186.226.227]. (S77719) [DM6NAM12FT022.eop-nam12.prod.protection.outlook.com 2023-06-01T17:48:19.869Z 08DB6279EB7055FC]


Received:from mysite.com (ec2.compute.amazonaws.com [myServerIP]) by mx.zoho.eu
    with SMTPS id 1685638370381990.8083428308522; Thu, 1 Jun 2023 18:52:50 +0200 (CEST)
Message-ID:<>
Date:Thu, 1 Jun 2023 16:52:49 +0000


Letters that I wrote to zoho tech support are completely ignored. I hope they will answer at least here, because we are already ready to change the mail service, cause we are losing customers.