550.5.1.1 - Not our customer


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"550.5.1.1 - Not our customer". One of our users is getting this bounce when sending to an individual at HP. Note that this is not consistent; sometimes the email makes it through while other times it will bounce back with that error. It appears to be a very generic error, encompassing everything from a typo, virus or trojan, to not having authentication enabled.

This is not happening with any other email sent to an address at XYZ Company. They are a Fortune 500 corporation so I'd like to think they've at least got their email setup correctly.

Any input greatly appreciated. Little relevant information is within the Header.

The exact error returned is:

----- The following addresses had permanent fatal errors ----- <firstname.lastname@company.com>

----- Transcript of session follows ----- .. while talking to smtp.company.com
>>> RCPT To:<firstname.lastname@company.com>
<<< 550 5.1.1 Not our customer