Mailer for use with DOS-based palmtops

As a collector of DOS-based handhelds and palmtops I am of course always on the lookout for software which would allow me to use these ancient computers productively. And one of the really cool things is of course to be able to read and answer mail on the go, using your Palmtop and a mobile phone. However, so far I haven't found the ideal program, which, for me, means:

Free
Certainly as in free beer, but with internet protocolls constantly changing it would be nice to also have access to the sourcecode so that, should the program become abandonware, I would be able to modify it myself.
APOP
I currently get my mail from an APOP account, so it should be able to speak this protocoll.
SMTP after POP
I send my mail using GMX, which as its most simple authentification method offers SMTP after POP, i.e. you need to download mail first and then can send from the same IP. Of course more advanced authentification methods would also be nice.
MIME
Meaning it should at least be able to decode quoted-printable and base64, and to convert at least iso-latin-1 and utf-8 into whatever codepage seems adequate for the palmtop.
TOP
It should be possible to download the headers (which is what the POP3 TOP command does) of all new mails only, then browse the headers and only download selected mails. As System-administrator I get loads of mails which, while I will need to read them eventually, do not warrant expensive GSM-time for download.
UIDL
It should be possible to synchronize the local mailbox with that on the POP-host, e.g. by deleting mails on one host which have been deleted on the other, or by downloading new mails only. This is what the POP3 UIDL unique id listing command does.
Driver
Using a proprietary driver for internet access can have its benefits (as in the case of Post/LX, which uses WWW/LX, which is th only application for the HP200LX capable of using the IR-Port), but in general it is better to use something like the Watcom Stack so that the same programms will work with SLIP, PPP, and Ethernet.

In the following I will list a number of MTAs (mail transfer agents), mail-readers, news-readers and similar programs as well as their capabilities (according to the documentation).

Comparison of different DOS-based mail-programs
Post/LX Nettamer lxmta 2.9b73 popsmt v0.5 fdsmtpop cc:lxpop 2.01 PNR 4.3b2 Yarn Goin' Postal
Licence Crippelware, US $79 Nagware, US $35 Open Source Free (Beer) GPL Open Source Open Source ??? Free (Beer)
Inbox Format MMDF UUPC, ... MMDF MMDF, mbox, bare format news files
Outbox Format RFC822 RFC822, FreeEmacs, Pegasus, UUPC RFC822 RFC822
POP3 MTA x x x x lxmta lxmta - x
TOP size limit -
UIDL - -
APOP x x
IMAP4 x -
SMTP ESMTP Cram-MD5, Login, Plain
SOUP
NNTP x
Reader
Driver