When one of my users sends email to an external email address they get:
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<SERVER.DOMAIN #5.5.0 smtp;550-Verification failed for <email@example.com>>
This has happened 4 times. I can send email from the users PC using his email account to my HOTMAIL address and that works OK. I can also send mail to the same external address from my PC using my email account and it works OK. But when I send mail using my PC and his email account to the external email address I get the same error.
The error message is coming from my exchange server. If this were a DNS issue surely I wouln't be able to send mail from my email account. Hope this makes sense.
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