Speaking on Deep Background, the Press Secretary whispered:

Look at that, a PalmOS app that does exactly what you're looking for.
Doesn't seem to have been too difficult to find.

I looked at SnapperMail. It's too early for me to recall why
it didn't fit the bill [caffine, STAT!] but it didn't..

It may have been the APOP issue...

And there's Lonelycat Profimail .. Dave Farber uses it all the time
these days, looks like.