You need to grant the user or group rights to use the profile. They need to be added to the msdb database and then you will see them available in the mail wizard when you are maintaining security for mail.
Read up the security here: http://msdn.microsoft.com/en-us/library/ms175887.aspx
See a listing of mail procedures here: http://msdn.microsoft.com/en-us/library/ms177580.aspx
Example script for 'TestUser' to use the profile named 'General Admin Mail'.
USE [msdb]
GO
CREATE USER [TestUser] FOR LOGIN [testuser]
GO
USE [msdb]
GO
EXEC sp_addrolemember N'DatabaseMailUserRole', N'TestUser'
GO
EXECUTE msdb.dbo.sysmail_add_principalprofile_sp
@profile_name = 'General Admin Mail',
@principal_name = 'TestUser',
@is_default = 1 ;