It should be easy to attach, say, every file in a directory to a message using Mutt.
Googling, mashing keys, reading the fucking manual, etc.
(If you've re-bound any of the default keys, this may be wrong by a character or two.)
After you hit a to attach a file, you can begin to
type a path (for local files), or press ? to get a
list of mail directories. Once you have typed part of the path, you
can hit tab to get a list of possible completions. There's no
mention of it, but you can tag files in this list with
t.
Use these tags to attach the files you want. You can't type a
wildcard and have it automatically attach matching files, but if you
do type a wildcard, Mutt will filter the list and only show you the
files whose names match the wildcard pattern. You can then tag them
all by mashing t real seriously.