I’ve been using either Mozilla email or Thunderbird
for some time now but have found an area they are lacking.
Namely, exporting. If, for example, I want to export all of my
email so I can store it while reformatting my hard drive I’m
left up the creek without the proverbial paddle. Neither
Mozilla email client can export email. So what are you supposed
to do? I don’t know. Copy the folders?
Drop me a line if you know of a way of exporting then
importing back in. By they way, after using both for awhile, I
think Thunderbird runs better. YMMV. FWIW.