Email agent infrastructure iRedMail
So far we understand the basic components of a mail system. Let's focus on iRedMail. Which programs are used as the mail components? Let's have a look:
- all - Overview
- MxAReceive - Email from external sender to local recipient
- MxASendLocal - Email from local sender to local recipient
- MxASendExternal - Email from local sender to external recipient
- MxADownload - Read E-Mails
MTA: postfix server with one filter
Postfix is the heart for incoming and outgoing emails. It doesn't offer any mailbox access but can pass the emails to a MDA server. A very important part of postfix is to protect us from spam and dangerous emails. This is done with some internal checks by postfix but also with external filters. iRedMail has one external policy filter (iRedADP) and one external content filter (Amavis new). All those filters decide if an email is accepted, rejected or marked. We will see later in more details how things are filtered. Read more about postfix if you like:
Where is cluebringer?
iRedMail installs cluebringer as a second external policy filter for grey listings but debian jessie has removed this program. That's why this documentation ignores cluebringer.
MDA: dovecot server with a filter
Dovecot is the heart of the mailbox. iRedMail default configuration: Postfix hands over e-mails to dovecot through the local delivery agent (LDA). Emails are stored on the server in the maildir format and can be accessed with IMAP or POP3 with an encrypted connection over TLS.
Sieve filter
Sieve is a general email filtering language not only for dovecot. The project pigeonhole implements sieve into dovecot. Incoming messages can be delivered to specific folders, forwarded, rejected, discarded, etc.
iRedMail default configuration: move spam to junk folder and handle vacation. Read more about sieve if you like:
MSA: postfix with dovecot sasl
Sending emails is done through encrypted SMTP Auth connection on tcp port 587. Dovecot SASL communicates with the MUA and hands over the email to postfix provided that username and password are valid.
SPF & DKIM
I'll talk later about SPF & DKIM. It's essential you send emails from your iRedMail server. Otherwise some SMTP server might mark your emails as spam!
MUA: roundcube
You can use any mail client program you like. iRedMail installs by default a webmail called "roundcube". This program is written in php and runs server side accessed by apache webserver. Open https://[yourDomain]/mail in your browser, enter email address & password and you'll have full access to your emails.