There's two other considerations about which mail program to use:
1. Is it secure? Does it have a nasty tendency toward being
infiltrated by viruses or trojans? If you choose Outlook or Outlook
Express, you're not just asking for trouble, you're rolling out a red
carpet for it, and sending engraved invitations. Eudora is somewhat
more secure, but there have been several different reported
infectious agents. Most other mailers are ignored, for various
reasons.
I use Pegasus myself. Because of its structure, it has proven immune
to everything so far. However, it's HTML rendering is far from
robust. So if you have correspondents who are rudely mailing HTML
pages as mail, you may not be able to read their scratches. (Better
to encourage them not to do it, anyway.)
2. Can it be interfaced to encryption software? PGP can be
interfaced very easily to both Outlook and Eudora. There is a free
third-party plug-in for Pegasus that is so-so. To find out if there
is a plug-in for other mailers, please look at
http://www.pgpi.org/products/tools/search/ for more info.
In a day and age where spying on people's email is becoming ever more
common, this is something that should be considered. In my own
experience, once committed to a email program, it's very hard or
impossible to convert all the saved messages to another program. So
choose wisely.
E.