If the account is IMAP and the account setting are not to store messages on this machine then there is no inbox file.

MSF files are in MORK format and ostensibly can be read with a script, but the effort would be significantly more that an unread email count is worth I would think.

Matt said

the effort [to read msf file] would be significantly more that an unread email count is worth I would think.

wognatn said

Matt said

the effort [to read msf file] would be significantly more that an unread email count is worth I would think.

Thanks, Matt. A little reading on MORK format convinces me you're right.

MORK is also the format of the address book files That was my conclusion when I tried to extract information from them.

I have a working check for new messages. As predicted, it was more effort than it was worth. In the unlikely event that anyone is interested ;) I'd welcome improvements and corrections.

It seems that unread messages result in a tag (^94=1) near the end of INBOX.msf. When any new message in that inbox is read or previewed, (^94=0) is appended. So the following works for me to check for new messages:

[loop over all accounts] tac /path/to/INBOX.msf | grep -m 1 '(^94=.)' | grep -v '(^94=0)' && [new mail action]

This is useful.

Any pointers to articles on how to make this part of my local setup (I'm on Win 10...) It would be a bit of a hack to get Msys2 + minnty etc to do all that.

I'm yet to dive into scripting/macros/aliasing (etc) for Thunderbird

I found no documentation, it's all trial and error based on Matt's answer above. There's a little more detail here.