I just started playing around with the Masked email setting and to see it's not something I would choose to use. FM chooses the local part of the email address. That's probably why you need a description to remind you what it is for. I think I like my way better when I overload a single alias (e.g.,
foo@mm.st) with something appropriate (e.g.,
example@foo.mm.st) and take advantage of FM's fuzzy folder matching to handle the filtering for me.
It's also not clear to me how you send masked email addresses. As best as I can
you need to create a sending identity for each one of these things. It's not automatic. That could really will clutter up the compose "from" drop down menu (speaking of sending identities, found another new "feature" but I'll post that under a separate thread).
Update:
Just noticed the previous post about being able to reply to these things if you don't need to send from them originally.