Exchange 2007 Standard, I just took over this site and they are only on SP1 so I will update them as soon as I can. The issue They don't receive email from a particular domain, this is a mailing list. They only have Exchange's spam filtering enabled. I've checked the smtp receive logs and can find no trace of the sender's IP or domain and that log appears to show when someone is blocked due to being blacklisted, they don't show up there nor anywhere else. I have not gotten info from the sender that they received a bounce-back but since it's a mailing list so I'm not sure they have looked or bother with bounce-backs, I'm in the process of trying to find out. They sender's IP is not on a black list. The only thing I can see is that the sender does not have a reverse DNS setup. The documentation I read says 2007 uses that to increase the sender reputation level, it's doesn't say it blocks outright because of it but I'd like to verify that. Also, if I add their IP to the approved IP list will that bypass a reverse DNS check? Should a block due to reverse DNS show up in the receive log?