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Postfix is a popular open-source mail transfer agent (MTA) used on Linux-based servers to route and deliver email. It is also used to receive incoming emails from remote servers. However, in some cases, Postfix may stop sending emails, either due to misconfiguration or because of an issue with the server.
However, the good news is that the problem is fixable, and the worst-case scenario is you have to go through the hassle of contacting a system administrator. So without wasting any more time, dive in to see what is causing the problem and how it can be fixed.
What Does Postfix Not Sending Mail Mean
Postfix not sending mail means that you’re trying to send an email to someone; however, it isn’t being received by the recipient. This can be divided into two causes: your email is being sent but isn’t routed to its correct destination, or your email is not being sent at all.
This usually happens if you haven’t configured the server settings of Postfix correctly or your client settings aren’t what they’re supposed to be. Moreover, your server might’ve gotten blacklisted.
Whatever the problem may be, it won’t get fixed all by itself. So unless you resolve it, you won’t be able to send anyone emails through Postfix.
Causes For Postfix Not Sending Out Mails
Before we get to the troubleshooting part, we’ve listed out some of the most common issues that might be the reason why Postfix isn’t sending emails.
Reason 1: DNS Settings Configured Incorrectly
Suppose Postfix’s DNS settings are not configured correctly. In that case, you might encounter various issues, including emails being sent to the wrong destination or sometimes not being sent at all.
That is because Postfix won’t be able to identify the server it is trying to communicate to. Hence It is important to ensure that the correct ports are open for Postfix to be able to send emails.
Reason 2: Check Client Settings
If the issue with your Postfix not sending out mails still persists, then it is likely that the root of the problem lies with the email client. It is important to ensure that the client is correctly configured with the correct SMTP settings.
A good practice would be to go through the configuration files as well as log files to see if something is causing an error and then work on fixing it.
Reason 3: Check If Your Server Is Blacklisted
There are several online services you can use to check if your server’s IP address is blacklisted. Some of the most popular services include MXToolbox, IP Void, Spamhaus, and Project Honeypot.
To use these services, enter the IP address of your mail server into the search field, and the service will then check if it’s listed on any blacklists. Most of these services also offer additional information about why your IP address may be blacklisted and provide suggestions for resolving the issue.
Possible Fixes to Postfix Not Sending Mail
To make it easy for you, so you don’t have the scour the internet for bits and pieces of information, we’ve listed all the solutions in one place. Go through them individually and see if it fixes the problem for you, which they hopefully should.
Solution #1: Check Log Files
When Postfix stops sending emails, the first step is to check the server’s log files for any errors. Log files for Postfix can be found in /var/log/maillog. If there are any errors, they should be addressed first before attempting to solve the issue. You can check for log files by typing in the commands:
/var/log/mail.log
/var/log/mail.err
/var/log/daemon.log
If there’s an error, you’ll easily be able to identify it.
Solution #2: Check Configuration Files
The configuration files for Postfix can be found in the /etc/postfix/ directory. To view the files, use the ‘cat’ command to display the contents of the file. For example, $ cat /etc/postfix/main.cf This will output the contents of the main configuration file.
You can also use the ‘less’ command to view the contents in a more user-friendly manner. For example, $ less /etc/postfix/main.cf This will open the file in a paginated format and allow you to scroll through the contents. Try searching for an issue in these files and if you don’t find one, move on to the next step.
Solution #3: Configure DNS Settings
Execute the command “telnet gmail-smtp-in.l.google.com 25” on your mail server to verify if port 25 (outbound) is blocked. If it’s blocked, you’ll see something like
Trying 2607:f8b0:400e:c06::1a…
Trying 74.125.195.27…
telnet: Unable to connect to remote host: Connection timed out
If port 25 is blocked, you can try using an alternate port, such as port 587, which is often used for email submission. Additionally, you can contact your ISP or network administrator to ask for port 25 to be unblocked.
Solution #4: Configure Client Settings
There might be something wrong with your client settings which may be causing Postfix not to send emails. There are several ways to check the client settings on Postfix.
- Check the main.cf file: The main.cf file is located in the /etc/postfix directory. It contains all the configuration settings for Postfix. You can view the settings by running the command “cat /etc/postfix/main.cf”.
- Check the master.cf file: The master.cf file is located in the /etc/postfix directory. It contains all the configuration settings for the Postfix master daemon. You can view the settings by running the command “cat /etc/postfix/master.cf”.
- Check the Postfix log files: The Postfix log files are located in the /var/log/maillog directory. You can view the log files by running the command “cat /var/log/maillog”.
- Check the Postfix configuration utility: You can check the configuration settings for Postfix by running the command “postconf -n”. This command will display all the configuration settings for Postfix.
Go through all these files and see if something isn’t configured properly. The process might be detail-oriented, but it will definitely help you identify the problem.
Solution #5: Contact The System Administrator
If all of the above steps have been completed and the issue with Postfix not sending emails persists, it is likely that there is an issue with the server itself.
In this case, it is best to contact the server’s administrator or a qualified system administrator for assistance. You can also try restarting the service to see if it fixes the issue by typing in the following command: sudo service postfix restart
Conclusion
Postfix sometimes stops sending emails because of various configuration issues or misconfigurations. It may be due to the wrong settings, incorrect SPF record, DNS settings, SMTP authentication, or other related issues.
While the problem might sound complicated, the good thing is it can always be fixed by tinkering here and there with some settings.
