From the Send Mail - Select Name dropdown
The (new) All Alts menu gets positioned such that a large part of it is off the top of the screen - I'd estimate maybe half, as it displays 16 1/2 names.
The bottom edge of the submenu is fairly high up the screen, looks like it may be anchored by it's bottom-left corner?
Also the menu contains names of Alts that have previously been deleted from Postal's database, and I did see one Alt listed twice (with different levels)
The Delete subsubmenu of All Alts only lists (valid) Alts on your current server for possible deletion, so these invalid entries can't be deleted from there.