We don't do anything to email, so it's unlikely to be Webroot interfering.  A 550 error means that the mail server on the other end rejected the message for some reason, so the mail at least got there before being bounced back.  Is there any more text to the error message that might elaborate on why?

 

Another way to confirm that it's a problem on their end would be to try sending an email from another computer and seeing what happens.

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