Hi,
this will describe the steps to setup a MailRelay for internal use the accepts SMTP Mails and relay it over a secure TLS connection with authification to an external mail provider on top of Debian 8 Jessie.
Install Postfix, after installation the basic configuration starts
root@devdebt ~ # apt-get install postfix
+---------------------------¦ Postfix Configuration ¦---------------------------+
¦ Please select the mail server configuration type that best meets your needs. ¦
¦ General type of mail configuration: ¦
¦ Satellite system X ¦
+-------------------------------------------------------------------------------+
Set the hostname of your local mailrelay (usually $HOSTNAME)
+------------------------------¦ Postfix Configuration ¦-------------------------------+
¦ The "mail name" is the domain name used to "qualify" _ALL_ mail addresses without a ¦
¦ System mail name: ¦
¦ yourmailrelay.yourlocaldomain.local_________________________________________________ ¦
+--------------------------------------------------------------------------------------+
The mail server/relay of your provider
+------------------------------¦ Postfix Configuration ¦-------------------------+
¦ SMTP relay host (blank for none): ¦
¦ mail.yourmailprovider.org_____________________________________________________ ¦
+--------------------------------------------------------------------------------+
Handle for mails to postmaster and root
+------------------------------¦ Postfix Configuration ¦-------------------------+
¦ Root and postmaster mail recipient: ¦
¦ ______________________________________________________________________________ ¦
+--------------------------------------------------------------------------------+
The destinations which are NOT forwarded. For these domains postfix accept mails and deliver these mails to local accounts.
+---------------------------¦ Postfix Configuration +----------------------------+
¦ Other destinations to accept mail for (blank for none): ¦
¦ yourmailrelay.yourlocaldomain.local, localhost________________________________ ¦
+--------------------------------------------------------------------------------+
+------------------------------¦ Postfix Configuration ¦-------------------------+
¦ Force synchronous updates on mail queue? ¦
¦ <No> ¦
+--------------------------------------------------------------------------------+
Networks from which mails are accepted
+------------------------------¦ Postfix Configuration ¦-------------------------+
¦ Local networks: ¦
¦ 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.100.0/24_________________ ¦
+--------------------------------------------------------------------------------+
+-----------------------------¦ Postfix Configuration ¦--------------------------+
¦ Use procmail for local delivery? ¦
¦ <Yes> ¦
+--------------------------------------------------------------------------------+
+------------------------------¦ Postfix Configuration ¦-----------------------+
¦ Mailbox size limit (bytes): ¦
¦ 0___________________________________________________________________________ ¦
+------------------------------------------------------------------------------+
+------------------------------¦ Postfix Configuration ¦-----------------------+
¦ Local address extension character: ¦
¦ +____________________________________________________________________________¦
+------------------------------------------------------------------------------+
+------------------------------¦ Postfix Configuration ¦----------------------+
¦ Internet protocols to use: ¦
¦ All ¦
+-----------------------------------------------------------------------------+
Create a SMTP Authfile /etc/postfix/smtp_auth_passwd ($SMTP_PASSWD_FILE) for the authentication at your Mailprovider
mail.yourmailprovider.org sender@yourdomain.org:yourpassword
Create the authentification hash file and set permissions
postmap hash:/etc/postfix/smtp_auth_passwd chmod 600 /etc/postfix/smtp_auth_passwd.db
Enable Authentification
postconf -e 'relayhost=mail.yourmailprovider.org:587' postconf -e 'smtp_use_tls=yes' postconf -e 'smtp_sasl_auth_enable = yes' postconf -e 'smtp_sasl_password_maps = hash:/etc/postfix/smtp_auth_passwd' postconf -e 'smtp_sasl_security_options = noanonymous' postconf -e 'inet_interfaces = all'
Restart Postfix
systemctl restart postfix.service
Also edit /etc/aliases for forwarding local E-Mails as needed. After editing you have to call newaliases to build the forwarding database.
Michael