Postfix relay through Outlook (TLS)

Abstract

We take email for granted. It seems so easy. Just click the send button. But spam has made sending and receiving email a lot more complicated. This is especially true for people who like to run their own networks at home. If you are like me, you might have 1 or more physical machines running multiple virtual machines, not to mention multiple containers as well. All this network infrastructure needs to communicate with you somehow. After all, how do you keep tabs on whether or not your CRON jobs are successful? Email is the way. But sending email out from a home network without it being blocked at various points along the way can get complicated. We can go through the cost of buying a domain and email service, but who wants the cost? So how do we get the email through? This post explains how to configure Postfix to relay email through an Outlook account over TLS.

Disclaimer

This post is solely informative. Critically think before using any information presented. Learn from it but ultimately make your own decisions at your own risk.

Requirements

I did all of the work for this post using the following major technologies. You may be able to do the same thing with different technologies or versions, but no guarantees.

• An Outlook account (outlook.com, live.com, etc.)
• Ubuntu 18.04.1 LTS
• Postfix 3.3.0

Install Postfix

I’m not going to go into a lot of explanation. I’m simply going to state the steps and configuration I did which got everything working.

First thing you need to do is install Postfix.

$ sudo apt-get update
$ sudo apt-get install postfix mailutils

NOTE For the Postfix installation, when it asks for the “System mail name” value, it should be the same as the name of the server.

Configure Postfix Authentication for Outlook

Configure Postfix to login to Outlook’s SMTP server. This configures the server name, port, account id, and clear text password.

# Create the password file
$ cd /etc/postfix/sasl
$ touch sasl_passwd_outlook
$ chmod 600 sasl_passwd_outlook

Now edit the sasl_passwd_outlook file using your favorite editor. Make it look like Listing 1, replacing ACCOUNT_NAME and CLEAR_TEXT_PASSWD appropriately.

Listing 1 - sasl_passwd_outlook

[smtp-mail.outlook.com]:587 ACCOUNT_NAME@outlook.com:CLEAR_TEXT_PASSWD

Now hash the sasl_passwd_outlook file into a Postfix .db file

$ postmap sasl_passwd_outlook

Configure Postfix Email Mapping for Outlook

If user mike attempts to send an email from a server with the name bluegreensky, the default Postfix FROM address will be mike@bluegreensky. This is not good because if you try to relay this email through Outlook, it will be blocked since the FROM address does not match the Outlook account. To get around this, configure a regular expression mapping file that will change all local email addresses (like mike@bluegreensky) to the Outlook account email address.

First, create a generic map file that’s empty

$ mkdir /etc/postfix/map
$ cd /etc/postfix/map
$ touch generic_map
$ chmod 600 generic_map
# Hash the file into a *.db file
$ postmap /etc/postfix/map/generic_map

Next, create an Outlook map file that will change local email address to the Outlook account email address.

$ mkdir /etc/postfix/map
$ cd /etc/postfix/map
$ touch regex_map_outlook
$ chmod 600 regex_map_outlook

Now edit the regex_map_outlook file using your favorite editor. Make it look like Listing 2, replacing HOSTNAME - just HOSTNAME, not @HOSTNAME…don’t lose the @ character - and ACCOUNT_NAME appropriately.

Listing 2 - regex_map_outlook

/.+@HOSTNAME/    ACCOUNT_NAME@outlook.com

Now hash the regex_map_outlook file into a Postfix .db file

$ postmap regex_map_outlook

Configure Postfix TLS for Outlook

TLS must be used to connect to Outlook SMTP servers. During Postfix installation, a main.cf is created. It must be edited

$ cd /etc/postfix

Now edit the main.cf file using your favorite editor. In Listing 3 are the values you must add or update in main.cf. For each of the name/value pairs below, search main.cf to see if it already exists. If so, use my value below. If not, add my value to the end of main.cf.

Listing 3 - main.cf

# Outlook
relayhost = [smtp-mail.outlook.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_security_options =
smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd_outlook
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtp_tls_protocols = !SSLv2,!SSLv3,!TLSv1.1
smtp_tls_ciphers = medium
smtp_tls_mandatory_ciphers = medium
smtp_tls_security_level = may
smtp_generic_maps = hash:/etc/postfix/map/generic_map, regexp:/etc/postfix/map/regex_map_outlook

Restart Postfix

Restart Postfix so it picks up all the new configuration.

bash $ service postfix restart

Testing Postfix

If all goes well, Postfix restarted without any errors and is now configured to relay email from the server through the Outlook account. I typically test this with both mail and at.

# Test sending mail directly
$ echo "test email message" | mail -s "test email from server" some_email_address@someprovider.com

# Test sending mail through scheduler at
$ echo "echo \"gosh golly, it is AT\"" | at now

Do this testing, and see if you get the email your are expecting.

NOTE When testing with at, you will want to create a ~/.forward file with your email address so the results of the scheduled job are not delivered to your server’s local account’s inbox.

Summary

This post shows how to configure Postfix to relay email through an Outlook account over TLS. Sending email from a home network and have it not be blocked is tough. This configuration got me working. I hope it works for you.