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Updated A mail server's 101 (markdown)

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Jean-Denis Vauguet 2020-06-10 00:02:38 +02:00
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docs/content/a-mail-server's-101.md
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@ -19,19 +19,21 @@ The following components are required to create a [complete delivery chain](http
- MTA: a [Mail Transfer Agent](https://en.wikipedia.org/wiki/Message_transfer_agent) is the so-called "mail server" as seen from the MUA's perspective. It's a piece of software dedicated to accepting emails: either from MUAs or from other MTA (the latter task being symmetrical, meaning a MTA is also is capable of sending/transferring emails to other MTA, hence the name).
- MDA: a [Mail Delivery Agent](https://en.wikipedia.org/wiki/Mail_delivery_agent) is responsible for accepting emails from an MTA, but instead of forwarding it, it is capable of dropping those emails into their recipients' mailboxes, whichever the form.
There may be other moving parts or sub-divisions, but that's the big picture.
There may be other moving parts or sub-divisions. For instance, at several point specialized programs may be filtering, bouncing, editing… exchanged emails.
docker-mailserver provides you with the following agents:
In a nutshell, docker-mailserver provides you with the following agents:
- MTA: Postfix
- MDA: Dovecot
One important thing to note is that both programs actually handle multiple tasks. For instance, Postfix is both an SMTP server (accepting email) and an MTA (transfering email); Dovecot is both an MDA (delivering emails in mailboxes) and an IMAP server (allowing MUAs to fetch emails from the so-called mail server).
and with some specialized, companion programs to form a complete delivery chain (minus the MUA of course).
For both Postfix and Dovecot need to be accessible from the outside to act as servers, they expose themselves through TCP ports, which may be secured using different schemes.
> One important thing to know is that both the MTA and MDA programs actually handle _multiple_ tasks. For instance, Postfix is both an SMTP server (accepting email) and an MTA (transfering email); Dovecot is both an MDA (delivering emails in mailboxes) and an IMAP server (allowing MUAs to fetch emails from the so-called mail server). On top of that, Postfix may rely on Dovecot's authentication capabilities. The exact relationship between all the components and their respective or, sometimes, shared responsibilities is beyond the scope of this document. Explore the wiki to get more insights about the toolchain.
## About security, ports…
For both Postfix and Dovecot need to be accessible from the outside to act as servers, they expose themselves through TCP ports, which may be secured using different schemes.
### SMTP
A MUA sending an email to a [SMTP](https://en.wikipedia.org/wiki/SMTP) server communicates using data packets exchanged over a network that both the client and the server are part of. In the case of docker-mailserver, the server is Postfix. The MUA may be anything, and its submission/request is (most frequently!) performed as [TCP](https://en.wikipedia.org/wiki/Transmission_Control_Protocol) packets sent over the _public_ internet. This exchange of information may, or may not, be secured in order to counter eavesdropping.