Mo,
These are pseudonyms, aliases that point to actual accounts, SME creates them by default for every user you create, using the firsname and lastname entered in the username creation proccess.
For example:
Firstname: Joe
Lastname: Blogs
Username: joeb
Pseudonym 1: joe.blogs@domain.com
Pseudonym 2: joe_blogs@domain.com
You can create as many pseudonyms for a username as you wish, well as far as I can tell.
Cyrus Bharda