Ben McGinnes wrote:
Hello, A friend of mine is a die-hard user of the Windows MUA The Bat! (yes, the client name includes the exclamation mark). He does, however, wish to move to Linux at some point and is looking for a mail client which has comparable features to The Bat!
He's already tried Thunderbird and it doesn't meet his requirements, also GPG support (either directly or through plugins) is essential.
"GPG support" is the only functional requirement you've given so far. Nearly all actively maintained MUAs support that.
http://www.ritlabs.com/en/products/thebat/ https://en.wikipedia.org/wiki/The_Bat!
We could look at The Bat! documentation to try to guess what his other functional requirements are, but it would be more accurate and less effort for him to simply tell us what they are. (Admittedly, failure to articulate meaningful requirements is an endemic problem. That's when you pay a consultant to trick them out of you, instead of asking a volunteer-staffed mailing list.)