Bobcares

4 reasons for “unknown mail transport error” in Postfix servers

by | Nov 2, 2018

Emails are vital for online businesses. That’s why email errors are a nuisance for server owners.

At Bobcares, we often resolve many such email errors as a part of our Technical Support Services for web hosting companies.

Today, we’ll see what causes “unknown mail transport error” in servers and how we fix them.

What causes “unknown mail transport error” in servers

Postfix is a commonly used mail server in Linux servers. Many control panels like Plesk offers Postfix mail server as part of its installation.

Postfix can also be integrated with third party mail server providers such as SendGrid. But at times, Postfix can throw errors during mail delivery.

One such issue is when server owners report of mail delivery errors. We examine the mail logs and notice a lot of undelivered outgoing emails in the mail queue.

The mail logs at /var/log/maillog often show these errors:

postfix/error[12027]: 541B4649412: to=<user@domain.com>, relay=none, delay=113711, delays=193632/1/0/0.01, status=deferred (unknown mail transport error)

 

The major causes for this error are:

1. Postfix configuration issues

The main configuration file of Postfix is /etc/postfix/main.cf. This file contains the default Postfix settings such as transport settings, network, mail server IP and so on.

In cases of external mail server or other special requirement, custom settings have to be done in this configuration file. This include adding IPs that can relay through the server.

Any wrong entries in this configuration file can lead to errors in email delivery, such as  “unknown mail transport error”. Software updates or patches can also corrupt Postfix installation and cause errors.

2. File permissions

The mail queue, configuration file, filters and mail folders, all these need to have proper ownership and permissions for mail delivery to work fine.

Usernames and passwords are saved in the file /etc/postfix/sasl_passwd. This file should be readable by Postfix service and need to have proper ownership and permissions.

After adding entries to the password file, it should be mapped to a database file in postfix. The database and other related files should have the right access privileges.

3. Missing aliases

Email aliases usually refers to forwarders to various email accounts. It can happen that sometimes the aliases contain non-existent or invalid email accounts, giving out errors in email delivery.

4. Third party integration

Postfix can be integrated with third party mail servers like SendGrid, Mandrill, etc. For mails to relay through their servers, custom configuration has to be done in Postfix.

In some installations of Postfix, only alphanumeric passwords are allowed. If the SendGrid password is not in that format or there are any configuration mistakes, mail server will throw errors.

How to fix “unknown mail transport error” in Postfix servers

1. Fix configuration errors

The major reason for “unknown mail transport error” is the error in configuration file. We figure out the erroneous entries and correct them.

In cases where the Postfix configuration is corrupt, we rebuild the configuration files and repair the Postfix installation and confirm that mails are working fine.

2. Examine email aliases

If the error is specific to only specific email addresses or aliases, we examine those aliases and figure out the missing accounts. We update these aliases for the mails to work fine.

3. Permission and ownership updates

We cross-check the permissions and ownership of the related files and folders and update them so that Postfix service can access them and deliver mails without errors.

4. Reinstall Postfix

In cases where the error occurred after any software or package updates, we pinpoint the module or patch that caused the issue. We reinstall or reconfigure those to ensure successful mail functioning.

In the servers we manage, we conduct periodic server audits to confirm the success of software updates and functioning of services. For the upgrades we perform, we take actions to avoid such issues.

Conclusion

Email errors can be vexing for server owners. Today, we saw how our Outsourced Tech Support team easily fix the error ‘unknown mail transport error’ for our customers.

 

PREVENT YOUR SERVER FROM CRASHING!

Never again lose customers to poor server speed! Let us help you.

Our server experts will monitor & maintain your server 24/7 so that it remains lightning fast and secure.

SEE SERVER ADMIN PLANS

var google_conversion_label = "owonCMyG5nEQ0aD71QM";

0 Comments

Submit a Comment

Your email address will not be published. Required fields are marked *

Never again lose customers to poor
server speed! Let us help you.

Privacy Preference Center

Necessary

Necessary cookies help make a website usable by enabling basic functions like page navigation and access to secure areas of the website. The website cannot function properly without these cookies.

PHPSESSID - Preserves user session state across page requests.

gdpr[consent_types] - Used to store user consents.

gdpr[allowed_cookies] - Used to store user allowed cookies.

PHPSESSID, gdpr[consent_types], gdpr[allowed_cookies]
PHPSESSID
WHMCSpKDlPzh2chML

Statistics

Statistic cookies help website owners to understand how visitors interact with websites by collecting and reporting information anonymously.

_ga - Preserves user session state across page requests.

_gat - Used by Google Analytics to throttle request rate

_gid - Registers a unique ID that is used to generate statistical data on how you use the website.

smartlookCookie - Used to collect user device and location information of the site visitors to improve the websites User Experience.

_ga, _gat, _gid
_ga, _gat, _gid
smartlookCookie
_clck, _clsk, CLID, ANONCHK, MR, MUID, SM

Marketing

Marketing cookies are used to track visitors across websites. The intention is to display ads that are relevant and engaging for the individual user and thereby more valuable for publishers and third party advertisers.

IDE - Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.

test_cookie - Used to check if the user's browser supports cookies.

1P_JAR - Google cookie. These cookies are used to collect website statistics and track conversion rates.

NID - Registers a unique ID that identifies a returning user's device. The ID is used for serving ads that are most relevant to the user.

DV - Google ad personalisation

_reb2bgeo - The visitor's geographical location

_reb2bloaded - Whether or not the script loaded for the visitor

_reb2bref - The referring URL for the visit

_reb2bsessionID - The visitor's RB2B session ID

_reb2buid - The visitor's RB2B user ID

IDE, test_cookie, 1P_JAR, NID, DV, NID
IDE, test_cookie
1P_JAR, NID, DV
NID
hblid
_reb2bgeo, _reb2bloaded, _reb2bref, _reb2bsessionID, _reb2buid

Security

These are essential site cookies, used by the google reCAPTCHA. These cookies use an unique identifier to verify if a visitor is human or a bot.

SID, APISID, HSID, NID, PREF
SID, APISID, HSID, NID, PREF