Configuring the Windows 2003 POP3 Service for Multiple Domains

We've had some fun today setting up our existing secondary SMTP server to double up as a POP3 server for a new domain. Actually setting the POP3 service up is a doddle. It's also pretty simple to set up the MX records to get mail to actually arrive on the server. What we couldn't work out was why mail was just sitting in the SMTP queue and not being delivered to the drop directory. We were thinking things like it must be a problem with the DNS name, or service binding (the server has two NICs and about 10 IP addresses, and services incoming mail for about 15 domains).

Looking at the logs revealed little. Then I remembered, because we use Exchange for all our other email domains, we use LDAP routing on the SMTP servers to check whether the email account exists in AD before sending it to the Exchange server – a quite useful anti-spam measure, that stops the Exchange server getting nonsense emails. However, in this case we were setting up POP3 users using the password file method (its intended for hosting clients) so they had no account or email address in AD – so the SMTP server didn't know what to do. Turning this feature off (LDAP Routing) and restarting the SMTP service did the trick, and mail instantly arrived in the appropriate POP3 box.

The final thing we implemented was email domain quotas. This means the whole domain shares a quota, rather than each user being limited to a certain amount. Again this is made slightly trickier by using the password file method. First, you have to create a local account on the POP3 server – we've named ours after the corresponding domain. Then, enable disk quotas on the volume containing the POP3 boxes (C: if you haven't changed anything). Then add a new quota entry for this new user – 10MB per mailbox is generally the case. Then use the WINPOP utility to create a quota file for one of your email accounts, and associate this with the user account as follows:

      WINPOP createquotafile 
         user@domainname.com /user:useraccount
   

This will create a quotafile in the corresponding email accounts mailbox folder – copy this file and put it in each mailbox you create that this quota applies to, and the quota will apply to all those boxes.