How to configure Postfix to use Gmail SMTP on Ubuntu 18.04 & 16.04

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In this article we are going to configure Postfix to relay mail through Gmail’s SMTP server on Ubuntu 18.04 & 16.04. If you want to use a SMTP server other than Gmail, please see How to configure Postfix to use an External SMTP Server.

Prerequisites

If your Gmail account uses 2-Step Verification, you must create an application specific password.

If you’re not using 2-Step Verification, please ensure that your Gmail account is configured to allow less secures apps.

1. Install Postfix

If you’ve already installed Postfix, skip to step 2.

Let’s update the package database first.

sudo apt-get update

Install mailutils, which will automatically install Postfix.

sudo apt install -y mailutils

On the first Postfix configuration screen, select OK by pressing TAB and ENTER

Select Internet Site and press ENTER.

System mail name should be your domain name eg. example.com, press ENTER.

Package should now be installed.

2. Configure Postfix

Edit the Postfix configuration file.

sudo nano /etc/postfix/main.cf

Find the following line relayhost = about 6 lines up from the bottom of the file and delete it.

Add the following to the end of the file.

/etc/postfix/main.cf
relayhost = [smtp.gmail.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtp_use_tls = yes

Save file and exit. (Press CTRL + X, press Y and then press ENTER)

3. Create Password and DB Files

Create the sasl_passwd file which will store our credentials.

sudo nano /etc/postfix/sasl_passwd

Insert the following:

/etc/postfix/sasl_passwd
[smtp.gmail.com]:587 [email protected]:password

Replace username and password with your own.

Save file and exit. (Press CTRL + X, press Y and then press ENTER)

Create a hash database file for Postfix with the postmap command.

sudo postmap /etc/postfix/sasl_passwd

There should now be a file called sasl_passwd.db in the /etc/postfix/ directory.

For added security, we will only allow root user to read and write to sasl_passwd and sasl_passwd.db

sudo chown root:root /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
sudo chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db

4. Sign Certificate

Now we are going to create the certificate.

cat /etc/ssl/certs/thawte_Primary_Root_CA.pem | sudo tee -a /etc/postfix/cacert.pem

There should now be a certificate file called cacert.pem in /etc/postfix

5. Send a Test Mail

We’ll now send a test email message. Make sure to replace [email protected] with your own email address.

echo "Test Email message body" | mail -s "Email test subject" [email protected]

Don’t forget to check your spam folder.

If you still haven’t received any mail, check the mail error log.

sudo tail /var/log/mail.log

If the mail log is empty or doesn’t exist, try parsing the syslog. This will return the last 50 entries for postfix.

sudo tail -f -n 50 /var/log/syslog | grep postfix

If the syslog is empty and you still haven’t received any test email, it’s possible that the test email was rejected by the recipient server. You should check to see if anything has bounced back to your mail folder.

sudo less /var/mail/$(whoami)

Press uppercase G to scroll to the bottom of the file and lowercase q to quit. The $(whoami) variable returns the currently logged in user.

Note: Sending Mail to Your Own Domain

If you ever intend to send email from postfix to your own domain, [email protected] for example, postfix may need some further configuration. Please see article Can’t send mail to own domain. Postfix: status=bounced (unknown user: “user”)

Let me know in the comments if this helped. Follow me on Twitter, Facebook and YouTube.

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10 replies

Rather than install mailutils (which also installs MySQL, which I do NOT want on these servers), I simply installed postfix first, then installed bsd-mailx. Everything is working! Since this is only to send me alerts from monit, fail2ban, cron, etc., I didn’t need anything more. I have this page bookmarked. Thanks!

I am hoping to do something like:
1- Use postfix to get my ‘inbox’ from gmail,
2 – Use dovecot to serve my local mailbox to my client,
3 – Use thunderbird as my mail client.

Why? I would like to store all my email on my Ubuntu server, to take advantage of offline storage, improved filters, improved security. Sorry if this is out of scope for this page, but it looked so promising. Perhaps somebody can send me to a page in that direction.

I can successfully send mail from the command line on my 17.04 Ubuntu server.

Sounds interesting. I haven’t used Dovecot before though it’s certainly on the list of guides to do here. If you have Postfix working you’re halfway there. I recommend getting started on the excellent DigitalOcean guide: How To Set Up a Postfix E-Mail Server with Dovecot. You may also consider registering your own domain and forwarding your Gmail there. Best of luck!

Sep 17 10:31:11 ubuntu postfix/local[4540]: 0AAEE5606B6: to=, relay=local, delay=0.89, delays=0.57/0.01/0/0.31, dsn=5.1.1, status=bounced (unknown user: "irvanmaulana338") Sep 17 10:31:11 ubuntu postfix/cleanup[4538]: A5DFA5606C1: message-id=<[email protected]> Sep 17 10:31:11 ubuntu postfix/bounce[4541]: 0AAEE5606B6: sender non-delivery notification: A5DFA5606C1 Sep 17 10:31:11 ubuntu postfix/qmgr[4308]: A5DFA5606C1: from=<>, size=2046, nrcpt=1 (queue active) Sep 17 10:31:11 ubuntu postfix/qmgr[4308]: 0AAEE5606B6: removed Sep 17 10:31:12 ubuntu postfix/local[4540]: A5DFA5606C1: to=<[email protected]>, relay=local, delay=0.54, delays=0.27/0/0/0.27, dsn=2.0.0, status=sent (delivered to mailbox) Sep 17 10:31:12 ubuntu postfix/qmgr[4308]: A5DFA5606C1: removed

I got this, why is bounced?

It works ?. One thing, I think mailutils install steps have changed in the new version, you might want to update the post.