Anne Wilson wrote:
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]
If you open ports, you will see folks scanning them - it's inevitable. A
public mail server will attract interest from those wishing to exploit it.
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?
Those looking for relays would be more interested in the smtp port 25.
The IMAP port is the port you connect to to receive your mail. As long
as your imap server (dovecot, courier-imap) is fully patched and
presumably secure then you should be OK.
Advice - one potential weakness is that by default your username and
password is likely being sent in plain text (not a good idea!). Someone
could potentially intercept your username and password and access/use
your email account. If that username/password is also your system
account then potentially that could be compromised too.
There are a number of things you can do to harden your security. You
could set up an additional user account with nologin for email so if the
username/password does get compromised it's limited to purely email. You
could run imap services on a non-standard port (security through
obscurity), or firewall the connection to only allow trusted IP
addresses (works if you always conect from known trusted IP addresses).
None of these solutions are perfect, so probably the best method is to
encrypt the connection using SSl. See howto here (for postfix/dovecot):
http://wiki.centos.org/HowTos/postfix_sasl
Hope that helps,
Ned
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