+1 for Pegasus Mail. Note that the developer has been working on the 5th major version for quite a while now, version 4.x is not quite contemporary
in look&feel*. (Which is OK for me, but less OK for other people - especially as you come from The Bat!.)
I,
personally, also own and
primarily use a license for
Pandora Mail which I - incidentally - first saw
on DonationCoder. It has replaced The Bat! for me when RITlabs decided to use ribbon toolbars which I don't want to use. Pandora Mail 4.1 uses roughly 53 megabytes (plus the profile folder which can not
completely be moved off
%APPDATA% as far as I can see) of disk space, it seems to not have a portable mode (yet?). Of course, you should be fine with
90s GUI design... (you can configure some of that.) :)
(* screenshot: Pegasus Mail 4.7 on Windows 11)If you like Alpine (which is good software, I admit), other interesting command line clients for Windows include
NeoMutt and a few others, but note that usual "ported to Windows" software mostly requires jumping through quite a few hoops to use the file system over Cygwin... :)