Outlook 360 sent mail rejected

[Bill Paine 0]

Hello,  a couple of our users are having their emails rejected to a few of our clients.  I don't really believe that ESET is messing with our emails as they depart, but I'm hoping that someone has a solution.

Many of the rejection emails include something like this:

Quote

 

Subject: [SPAM] Mail System Error - Returned Mail with Subject: 327128

 

This Message was undeliverable due to the following reason:

 

Your message was not delivered because the destination computer refused to accept it (the error message is reproduced below).  This type of error is usually due to a mis-configured account or mail delivery system on the destination computer; however, it could be caused by your message since some mail systems refuse messages with invalid header information, or if they are too large.

 

Your message was rejected by gmail-smtp-in.l.google.com for the following reason:

 

     5.7.1 [65.20.48.74] Our system has detected that this message is not RFC

     5.7.1 5322 compliant: duplicate headers. To reduce the amount of spam sent

     5.7.1 to Gmail, this message has been blocked. Please review

     5.7.1  RFC 5322 specifications for more information. y5-20020a814b05000000b00354927dfb3fsi16628844ywa.50 - gsmtp The following attachments have been removed from the bounce message: 327128 MARTINEZ REVISED 2.jpg

 

[Marcos 5,460]

Please send a test email as per the instructions at https://www.mail-tester.com/ and provide me with a link to the results.

[Bill Paine 0]

Thank you for taking a look.  I'll also do this with the other users that have been having trouble.

https://www.mail-tester.com/test-h5pllcdcq

[Marcos 5,460]

The email is not recognized as spam by ESET Antispam. It appears that the misdetection has been resolved in the mean time.