We subscribe to the SBL/XBL list from Spamhaus, and the Combined list from NJABL.org, as well as use standard at-server spam resistant procedures.
You'll need to configure your mail client to pick up mail from the server using APOP (it may be listed as "secure" or some other safe-sounding option). Also, you must use a mail client capable of SSL encryption. Usually somewhere there's a setting for "port number," which should change to "995" automatically when you enable the encryption.
Much like setting up POP, except in this case, the encrypted authentication method required is called CRAM-MD5. SSL for IMAP uses port 993.
This still uses port 25, and SSL is available, but not required. However, to send a message to the mail server for delivery to an account not local to the server, you'll have to authenticate to the SMTP server, again using the CRAM-MD5 protocol.
When you make a secure connection (as explained above), your mail client will probably complain about the security credentials of the server being unknown to the client. In order to avoid the security cautionary note, your computer needs to have a copy of the certificate of the organization that has certified the mail server's certificate. Our mail certificate was issued by the Certificate Authority division of the Royal Grand Fenwick Internet Service Provider.