[CentOS] IMAP security

I have port 143 open so that I can get my mail when away from home. Occasionally, though, my router reports things like

Thu, 2008-03-27 02:00:11 - TCP Packet - Source:200.122.134.9,3821 Destination:88.97.17.41,143 - [IMAP rule match] Thu, 2008-03-27 05:39:49 - TCP Packet - Source:140.127.181.141,3461 Destination:88.97.17.41,143 - [IMAP rule match] Thu, 2008-03-27 16:10:03 - TCP Packet - Source:80.88.161.125,2352 Destination:88.97.17.41,143 - [IMAP rule match]

Looking at those addresses in whois, I don't see any good reason for these, and I'm concerned in case they are relays. Advice?

Anne