Symptoms
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After sending an email from one domain to another (both hosted on the same Plesk server), the email is not delivered and a bounce message is received:
Delivery to the following recipient failed permanently:
john_doe@example.com
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain example.com by mail.example.com [203.0.113.2].
An error occurred while sending mail.
550 Requested action not taken: mailbox unavailable or not local
Please check the message recipient john.doe@example.com and try again. -
Mail for the recipient domain is served externally (for example, at Gmail or Office 365).
Cause
Mail service of the recipient domain is enabled in Plesk/MailEnable.
Resolution
Disable mail service for the domain, mail of which is served externally, in Plesk at Domains > example.com > Mail tab > Mail Settings.