Running a small network on Windows Server 2003 hosting email via Exchange 2003, and using Symantec Mail Security 6.0 with Premium Antispam and with all the latest updates.
No problems with email communications since this was set up in 2007. But just since Monday one user is not receiving some specific external emails, and the people trying to email this person were getting bouncebacks with this data:
550 5.7.1 Requested action not taken: message refused
I have determined from the Mail Security Event Logs that at least some (hopefully all) affected emails are getting blocked by Maill Security's antispam filter. But I can't figure out why that would be. Some of the senders are people we've been in constant touch with for some time and some of their emails are going through to the affected user, and all emails seem to be going through to all other users. There is nothing onerous in the blocked emails - no attachments, no suspect message titles or text. A couple of the emails are from government domains. Although it wouldn't even make sense I checked to make sure our domain is not blacklisted, and it is not. Also, one of the emails was sent from a gmail account. I have sent a multitude of test emails from another gmail account to see if I can replicate the issue without success.
Am looking for any help in further troubleshooting this issue. Appreciate any and all input!