Serving e-mail

E-mail may just be the lifeblood of the Internet, unless you're younger than 25.

Various tools come together to provide what is generally termed an E-mail Server, and we bring together some of these key tools on OpenBSD.

Optional items, depending on your requirements may include:

• Authentication Database
• GUI Management Tool

The Mail Transport Agent (MTA)

With OpenBSD 4.6, OpenBSD released the beginnings of an MTA developed with the objectives and priorities of the project. SMTPD(8) (Simple Mail Transfer Protocol Daemon is developing with each OS release.

More commonly referred as the mail 'server', two major MTA's documented here are:

• Sendmail (included with the default OpenBSD install), and
• Postfix (a well regarded mail server, included with the OpenBSD ports collection.)

The MTA manages the storage and forwarding of messages. Delivery can be local (to local users) or by forwarding the message to another MTA. Custom configurations for MTA's can include:

• Proxy Mail Service
• Virtual User Accounts

Clients Access through POP3, IMAP Server

Your Mail Clients normally access their e-mail either through desktop clients (Mail User Agents) such as Microsoft Outlook and Mozilla Thunderbird.

Clients 'push' their e-mail to the MTA's for delivery, but pull their e-mail from other services on the 'server.'

Two major services for end-users to retrieving e-mail from a server is POP3 and IMAP. Various options are available with the default OpenBSD install, with additional alternatives provided in the ports collection.

• popa3d in the OpenBSD default install services POP3
• Courier Imap and UW Imap in the ports services IMAP
• Dovecot in the ports collection can service both POP3 and IMAP

Domain Name Server (DNS)

Ref: OpenBSD as a domain name server | Is my DNS a mess

A key infrastructure for email delivery, is Domain Name Services (DNS). For mail destined outside, or coming from the outside we are dependent on the Global DNS.

Your MTA Mail Server will need connection to a DNS server, to find out where to send e-mails, and it needs to be listed on the DNS system (so other Mail Servers can forward e-mail to your server.)

Common Fault:

When you can ping your mail host, but can't connect with SMTP, check your DNS setting (either /etc/resolv.conf or /var/spool/postfix/etc/resolv.conf)

Authentication Database

For a mail system servicing a small number of static users, it is sane to maintain user account details using text/hash database files (or ths host system accounts.) Large installations, with a high frequency of user changes may benefit from flexibility through a database server.

GUI Management Tool

Various tools exist to simplify an administrators workload through GUI toolsets, and allows delegation of various user creation, management responsibilities.

Postfixadmin is a wonderful Web GUI tool for managing your postfix/dovecot installation.