You can use any characters A-Z, a-z, 0-9, and these special characters: '_' (underscore), '-' (hyphen), and '.' (dot). Aliases are case-insensitive, so the address DrJones@pobox.com is identical to drjones@pobox.com.
Your aliases can be up to 80 characters long, but we recommend you make them shorter, to avoid misspellings and problems with other systems.