I'm guessing it might be related to the new 'play by mail' quest, but I and a couple of other people have had odd things happening when trying to send in-game mail with items attached to them.
The send dialog hangs and/or the mail doesn't get through and/or it gets through but without the attachments.
I've happily sent mail with attachments in previous quests so my guess is something got tweaked in there.
Ahhhhh... I've just realized what's changed. It used to be 'one item and one item only'... now we can send multiple items attached to a single mail. Great addition but seems to be buggy. Mails with nothing attached get through fine, mails with attachments remove the items from the inventory but don't get through.