I know there are a lot of threads on this, but I'm rather stumped. The problem is that a certain valid e-mail address, which I can e-mail to/from via Hotmail, always gives "Sender Verify Failed" on my cPanel servers. Both outgoing, and incoming (I have sender verification enabled). I tested it from a variety of servers, in two different data centers, with various Linux versions, some with Mailscanner/ClamAV, some without, etc. It really seems that Exim just can't verify this one address. I don't know the algorithm Exim uses for sender verification and haven't dug through the Exim source code yet (that's my last resort I guess), so I was wondering if any Exim gurus can shed any light before I whip out the source code. If it's of any relevance, this domain doesn't have an "A" record (no Web site), but it does have a valid "MX" record. I'll give the address here, because I know nobody can really help without it. Hopefully nobody will abuse this address, as it is a client of a client. Note, this address is on a Windows server, using some commercial e-mail server called MailMax 5.5. The address is: d r g at d r g e x c l u s i v e l y dot c o m. Thanks in advance for any assistance.