new e-mail alias: only one-char

[fuban]

hey there,

i want to migrate an existing email account to an isp3 installation. the account needs to have an alias with only one letter as local part. x@domain.com ... but ispconfig does not allow that: "Email address is invalid."
i haven't found an option or settings-file where to change that, is there a solution?

thanks, fabian

edit: found an answer here: http://howtoforge.com/forums/showthread.php?t=42869