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EE email requested stale question close.
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This issue just crept up in trying to send to an internet/external domain. Using an Exchange 2007 server this suddenly appeared with only sending to one specific domain. Receiving mail is no issue and sending to other domains does not generate this issue. Only one domain is causing this issue: #554 5.4.4 SMTPSEND.DNS.MxLoopback; DNS records for this domain are configured in a loop ##. <br />
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Is this an issue on my end, since I have had this server in place for many years and never had this problem, or is it on the recipient side?
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This issue just crept up in trying to send to an internet/external domain. Using an Exchange 2007 server this suddenly appeared with only sending to one specific domain. Receiving mail is no issue and sending to other domains does not generate this issue. Only one domain is causing this issue: #554 5.4.4 SMTPSEND.DNS.MxLoopback; DNS records for this domain are configured in a loop ##. 

Is this an issue on my end, since I have had this server in place for many years and never had this problem, or is it on the recipient side?

Sending email to a single domain generates a #554 5.4.4 SMTPSEND.DNS.MxLoopback bounceback

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Microsoft Outlook is a personal information manager from Microsoft, available as a part of the Microsoft Office suite. Although often used mainly as an email application, it also includes a calendar, task manager, contact manager, note-taker, journal, and web browser.