An odd question, maybe ... but is there a way of setting up POP3 to accept a compressed connection? and/or any mail readers that support such?
TLS can do compression in addition to encryption, though I'm unsure how widely implemented it is.
http://www.ietf.org/internet-drafts/draft-ietf-tls-compression-05.txt
There isn't really POP3-specific compression though.
You may well be able to use a VPN with compression - an ssh tunnel, compressed IPSec link, ppp compression, etc.
Craig Ringer
