In reguard the text files (newletter.txt, sysletter.txt, etc) used by Mystic (Linux) does case matter? I haven't noticed any issues, but it's nice to know these things.
Yes. For all filenames Mystic uses lower cased in case sensitive file
systems.
There are some very few places where case doesn't matter for compatibility reasons. Off the top of my head some of them are:
FILE_ID.DIZ importing
QWK and REP processing
Duplicate file scans
For all other places, case matters on case sensitive file systems.
The only exception to this rule that I can think of is in the case of DOS drop files. Mystic will create them in all uppercase, ie "DOOR.SYS", "CHAIN.TXT". I don't remember why but I think it was because of some issue with DOSEMU back in the 90s.
--- Mystic BBS v1.12 A29 (Windows)
* Origin: Sector 7 [Mystic BBS WHQ] (46:1/127)