Send Emails on Mac OS X with Postfix and a Gmail Relay

A quick howto setup Mac OS X and Postfix to use Gmail as a relay. Everything will need to be executed as root using sudo. If you just need to send emails try running sudo postfix start, and make sure to check your spam for emails – they will likely be flagged as they originate from a local mail server.

SASL Authentication

Connecting to the Gmail SMTP server requires both SSL and authentication. To set up authentication you will need to edit the /etc/postfix/sasl_passwd file.

sudu vi /etc/postfix/sasl_passwd

Update the contents to include the following. Note that enclosing hostnames with square brackets – [] – tells Postfix to avoid doing an MX lookup. Make sure to replace EMAIL with your email address, and PASSWORD with your Gmail password, properly escaping any colons in it.

[smtp.gmail.com]:587 EMAIL@gmail.com:PASSWORD

Use the postmap command to update the SASL credentials in Postfix.

sudo postmap /etc/postfix/sasl_passwd

Postfix Relay Configuration

Next we need to edit the Postfix configuration found in /etc/postfix/main.cf.

sudo vi /etc/postfix/main.cf

I was not able to route mail to the Gmail SMTP servers over IPv6, so force only IPv4 connections by searching for the inet_protocols key and updating the value.

inet_protocols = ipv4

If any of the following keys already exist in your configuration comment them out, and include the following at the bottom of the config file.

# Gmail SMTP relay
relayhost = [smtp.gmail.com]:587

# Enable SASL authentication in the Postfix SMTP client.
smtpd_sasl_auth_enable = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options =
smtp_sasl_mechanism_filter = AUTH LOGIN

# Enable Transport Layer Security (TLS), i.e. SSL.
smtp_use_tls = yes
smtp_tls_security_level = encrypt
tls_random_source = dev:/dev/urandom

Restart Postfix & Test

Restart Postfix as root, then send a test email.

sudo postfix stop && sudo postfix start
date | mail -s "Test Email" YOUR_EMAIL@gmail.com

If you don’t receive the test email, check the Postfix queue by running mailq or looking at the contents of /var/log/mail.log. Any errors that mention “SASL authentication failed” indicate that you may have entered an incorrect email/password combination, forgot to run postmap after updating the credentials, or need to Turn On Access for less secure apps in Gmail for your account.

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7 Responses

  1. Emso says:

    Thanks for the tutorial. It worked!

  2. Nathan says:

    I’ve been looking EVERYWHERE for an answer to this problem. I’ve tried so many different configurations. Yours is the one that worked. Thank you so much!

  3. J.J. Boomsma says:

    On macOS Sierra (10.12.5) it did not work. From gmail I received an “Undelivered Mail Returned to Sender” with a message:
    Action: failed
    Status: 5.5.1
    Remote-MTA: dns; smtp.gmail.com
    Diagnostic-Code: smtp; 530-5.5.1 Authentication Required. Learn more at 530
    5.5.1 https://support.google.com/mail/?p=WantAuthError i42sm247714ede.5 –
    gsmtp
    The main.cf is updated, the sass_passwd is created, The postmap /etc/postfix/sasl_passwd and the postfix has been restarted.
    What can I do more?

    • Justin Silver says:

      My first guess would be that the username or password is incorrect – just to double check the auth info goes into /etc/postfix/sasl_passwd (you have sass_passwd in your comments as well as the correct spelling). If the file is named correctly you might need to escape your password if it has any special characters (dollar sign, asterisk, etc) as they might not be interpreted correctly. Also check out the link in the error you are getting – there are a few troubleshooting steps on that page regarding two factor authentication, allowing “less secure” apps, or possibly unlocking your account.

      Good luck!

    • Mark Statkus says:

      @ J.J Boomsma – are you running MacOS Server too?

    • Plentipeppa says:

      Check over your files, I see in one instance you type sass_passwd.
      Next line you speaking about sasl_passwd.

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