Postfix is a free, open-source mail transfer agent (MTA) used to route and deliver email over the Internet. FastMail is a paid service that provides a secure, privacy-focused email provider supporting custom domains. This post details the setup instructions for using Postfix as a Send-Only SMTP server, using Fastmail, on a Ubuntu Linux 22.04 server.
init: 20240312)[email protected], the email address set up in FastMail to send emails from.
- host.example.com, the DNS name of your server (pointing to an unroutable private IP is fine)
- [email protected] is the account owner of the FastMail account.
- example.com is the domain from which we send emails.
- [email protected], the destination email we will test sending to.[email protected].
More details on the above can be found at https://www.fastmail.help/hc/en-us/articles/360058753394-Custom-domains-with-FastmailMX points to Fastmail and that SPF and DKIM are correctly configured at your DNS. Fastmail has a valuable dashboard on its Domains page with checkmarks for those settings.
Once properly configured, you will have “Your domain is correctly set up to send and receive mail!” on that domain’s dashboard on Fastmail.example.com domain using their outgoing SMTP services and app-specific passwords through Postfix.[email protected]. We will need this information later for the relay to work.[email protected] email alias to send messages and adapt the domain and the email address as needed.
Fastmail notes, “Every external program or app needs its own app password to access your information.” More details are available at https://www.fastmail.help/hc/en-us/articles/360058752854-App-passwords.
The Fastmail “server name and ports” are detailed at https://www.fastmail.help/hc/en-us/articles/1500000278342-Server-names-and-ports. We will follow the instructions for SMTP on port 465.Set Up -> My email address, then Add address, and then Create an Alias. Add [email protected], and on the next page, decide what you want to do “when a message is delivered to this address” and add a “Description.” You can also configure the “Advanced delivery preferences” and “Compose options” according to your needs.Stay Secure -> Privacy & Security. In the Integrations tab, create a New App Password. Name it postfix and give it only SMTP access. Copy and store this “postfix smtp app password” in a password manager for future use, as “this is the password for your app. Spaces and capitals donʼt matter. For your security we wonʼt show this password again”.hostname as a Fully Qualified Domain Main (FQDN).
To do so, sudo nano /etc/hostname and replace the value with host.example.com.
If your host is not publicly accessible (on a private network), add host.example.com in /etc/hosts with the local IP so the host can find itself and not attempt to do a DNS lookup.
A reboot is recommended, but you can also sudo hostname host.example.com until the next reboot.postfix) and adapt example.com to your domain.sudo apt-get update sudo apt-get install mailutils # during this step, you will be prompted to select the mail configuration that best matches your needs. # Select "Internet Site" as per the following dialogue: # "if a mail address on the local host is [email protected], the correct value for this option would be example.org" # As such, give it example.com
sudo dpkg-reconfigure postfix.
We will manually modify the configuration next.sudo nano /etc/postfix/header_check and add the following/From:.*/ REPLACE From: [email protected]
sudo nano /etc/postfix/sender_canonical_maps and add the following/.+/ [email protected]
root will function, given that it will try to contact [email protected]. Edit a new file sudo nano /etc/postfix/recipient_canonical and add to it:[email protected] [email protected]
sudo postmap /etc/postfix/recipient_canonical
root,) following details found in this post https://askubuntu.com/a/599513sudo nano /etc/postfix/sasl/fastmail with the below content, adapting the “postfix smtp app password” generated earlier. [smtp.fastmail.com]:465 [email protected]:apppassword
root user, using sudo chmod 400 /etc/postfix/sasl/fastmailpostfix to use the credentials using its lookup table management utility to create a /etc/postfix/sasl/fastmail.db file:sudo postmap /etc/postfix/sasl/fastmail
sudo nano /etc/postfix/main.cf and:myhostname to have our domain information (the DNS entry does not need to exist, but an unroutable network/private IP in your DNS will also work):myhostname = host.example.com
mydestination field so that all emails sent out are sent through the relay:mydestination =
inet_interfaces and make it loopback-only so that our postfix does not listen on any other active network interface:inet_interfaces = loopback-only
inet_protocolsinet_protocols = ipv4
smtp_tls_security_level and relayhost lines to avoid warnings, then add the following to the end of the file:relayhost = [smtp.fastmail.com]:465 smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl/fastmail smtp_sasl_security_options = noanonymous smtp_use_tls = yes smtp_tls_wrappermode = yes smtp_tls_security_level = encrypt
/etc/postfix/sasl/fastmail file we created earlier is referenced.
Additional details on TLS for postfix can be found at https://www.postfix.org/TLS_README.html.
Because we are not using port 587 (Fastmail recommends using port 465 for SMTP), we are using the wrappermode.sender_canonical_classes = envelope_sender, header_sender sender_canonical_maps = regexp:/etc/postfix/sender_canonical_maps smtp_header_checks = regexp:/etc/postfix/header_check
[email protected] map:recipient_canonical_maps = hash:/etc/postfix/recipient_canonical
postfix with its new configurationsudo /etc/init.d/postfix reload
[email protected]:# content and subject echo "Test mail content" | mail -s "Postfix Subject" [email protected]
tail -n 30 /var/log/syslog.
If all went well, you should have an entry with a status=sent value and looking similar to (###-ing variable content)postfix/smtp[###]: ###: to=<[email protected]>, relay=smtp.fastmail.com[###.###.###.###]:465, delay=###, delays=###/###/###/###, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as ### ### via ###)
[email protected] at your [email protected] email.
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