1 character username

[Divyank Turakhia]

How do i add a username with 1 character only. The problem is one of my
clients is using some outdated local mail server which allows usernames to
be only 20 characters. His domain name is 18 characters. The @ sign takes 1
character. that leaves only one chartered for his username. When i try to
add a letter username it gives me an error stating "illegal username".

Is there any way i can add a one character username??? some thing like
[EMAIL PROTECTED]

Divyank