Email - Postfix

About

Postfix ¹⁾ is a SMTP server, supporting LDAP, SMTP AUTH (SASL), TLS

The postfix installation installs also an alias to the sendmail command line.

Security / Privileges

• The SMTP Protocol Doc - the SMTP server rejects mail for unknown recipients.

SMTP servers need to decide whether an SMTP client is authorized to send mail:

• to remote destinations,
• or only to destinations that the server itself is responsible for.

Once a remote client is authenticated, a server generally give the same network privileges.

Relaying is allowed only for authenticated users, and IP addresses you specify in mynetworks.

Configuration

See Postfix - Architecture (Processes)

Respond

nmap -Pn -p T:25 server

Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-15 13:54 W. Europe Daylight Time
Nmap scan report for nico.gerardnico.com (xxxxxx)
Host is up.

PORT   STATE    SERVICE
25/tcp filtered smtp

Nmap done: 1 IP address (1 host up) scanned in 3.16 seconds

Parameters

mydestination

Which mail should be saved on the machine

• If you don't want to store email for a specific domain on the server leave it untouch

mydestination = $myhostname, localhost.$mydomain, localhost

inet_interfaces

postconf.5.html: Example of value and their consequence

• all

netstat -tulpn | egrep (master|:25)

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      5611/master

• 163.132.99.201, 127.0.0.1

netstat -tulpn | egrep (master|:25)

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      2413/master
tcp        0      0 163.132.99.201:25       0.0.0.0:*               LISTEN      2413/master

Mailbox

The home_mailbox parameter specifies the optional pathname of a mailbox file relative to a user's home directory. The default mailbox file is /var/spool/mail/user or /var/mail/user.

home_mailbox = Mailbox
# for qmail-style delivery (the / is required).
home_mailbox = Maildir/ 

where:

• Maildir separates messages into individual files that are then moved between directories based on user action.
• Mailbox stores all messages within a single file.

Virtual

Postfix - Virtual Aliasing (Email Redirect)

Sasl authentication

With Sasl:

• a remote SMTP client can authenticate to the Postfix SMTP server,
• the Postfix SMTP client can authenticate to a remote SMTP server

More Postfix - SASL (SMTP Authorization)

smtpd_forbidden_commands

default to (CONNECT, GET, POST)

List of commands that cause the Postfix SMTP server to immediately terminate the session with a 221 code.

Version

postconf mail_version
# or
yum info postfix

Log

• /var/log/maillog
• /var/log/messages – Contains global system messages, including the messages that are logged during system startup.

See:

• postconf.5.html = mail
• postconf.5.html = ${multi_instance_name:postfix}${multi_instance_name?$multi_instance_name}