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Some messages are failing with the error "Hop count exceeded - possible mail loop"

I am receiving messages into SpamHero, and they are showing in the Quarantine+. But, they are failing to send to my mail server. I am seeing this error when I look at the delivery logs:

status=bounced (host example-com-au.mail.protection.outlook.com[104.47.117.36] said: 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [SY3AUS99FT999.eop-AUS01.prod.protection.outlook.com] (in reply to end of DATA command))

This error happens if your mail server is not configured to accept the message for the user. Your mail server may be sending the message back out to the Internet, and through your domain's MX records (which likely point here to SpamHero). We then accept the message, filter it, and relay it on to your mail server again. Then this repeats until one of the servers decides to not accept the same Message ID over and over again.

To solve this problem, you must ensure your mail server is configured to accept these messages. It may be a user specific setting.

Last updated December 17, 2020