Add mail user disable sending option

[basmevissen]

Hi,

I was looking for a way to disable smtp access (to send e-mail over the server) from the control panel. There is a field "disablesmtp" in the mail_user table already.

This field needs to be added to the sasl2 sql query as well:
File /etc/postfix/sasl2/smtpd.conf:

sql_select: select password from mail_user where email = '%u@%r' and disablesmtp = 'n'

For now, this option needs to be set in the database directly using for example phpmyadmin.