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RadioReference.com Forums
If you've been reading the UDXF logs for any length of time, you will have seen the name 'Sailmail' - an email service for yachts. They usually use one of the many variants of PACTOR (1 through 4), and while there are packages that can copy this mode, I would imagine that the email contents are encrypted...
Anyway, this website lists all the stations, callsigns and frequencies - handy if you happen to tune this and wonder what it is...