The purpose of this guide is to establish a virtual mail system that can handle multiple domains with a variety of different interface options. This is not intended to be used by the average user who is looking for a mail client, this is a full-scale Mail Transfer Agent (MTA) intended for individuals who are hosting their own domains and/or need to provide support for virtual domains.
By the end of this guide, an easy method to manage a mail server that supports the following features has passed the revue:
- Web based system administration
- Unlimited number of domains
- Virtual mail users without the need for shell accounts
- Domain (specific) user names
- Mailbox quotas
- Web access to email accounts
- IMAP and (very optional) POP3 support
- SMTP Authentication for secure relaying
- SSL for transport layer security
- Strong SPAM filtering
- Anti-Virus filtering
- Log Analysis
The real plus is that all of this is managed by a single database.
This section outlines a system setup (a multi-server implementation) as well as the core packages that were used. This is a MUST READ before reading on any further (don't worry, it's short).
Mailboxes are stored on a normal filesystem and thus needs a user and group for security.
www-apps/postfixadmin and www-servers/apache were key tools in getting through testing and getting this to hang together. While the details of an Apache/PHP setup are not here, there is good information in here all the same.
mail-mta/postfix will be coupled to a database backend allowing virtual users on multiple domains.
net-mail/courier-imap will be coupled to the same database.
Having a mailserver that relays local mail is good enough for most, being able to relay mail after authentication is extremely handy.
Now that a basic mailserver has been setup, web access can be both useful and helpful during testing.
Securing the mail server with SSL certificates.
Signing all outgoing messages with verification keys to prevent ending up in the junk box.
Using default Postfix configuration options, the server gets some performance tweaks and security settings.
Defending against spam using Amavis, Spam-assassin and ClamAV for virus protection.
Always important is monitoring. To do so AWStats is used to get a useful overview of passed messages.