How to fix ‘550 5.1.1 : Recipient address rejected’ error in Exchange and Postfix servers
In our role as Website Support specialists for web hosting companies, we’ve seen internet users sending emails to certain recipients encountering the error:
550 5.1.1 <email@example.com>: Recipient address rejected
This error is associated with recipients whose emails are hosted in Exchange and Postfix servers. Today we’ll discuss the reasons for ‘550 5.1.1’ error and how to fix it.
How to fix error ‘550 5.1.1 : Recipient address rejected’
This 550 error can happen due to two main reasons:
1. Issues related to the recipient server
The common issues that can happen with the recipient end are:
a. Recipient address wrongly specified in the email
Many often, the error is caused by a very simple reason – incorrect email address given in the email. Sometimes a typo in the address can often lead to emails bouncing.
If the email is addressed to a non-existing account or account that is no longer in use in the recipient server, the recipient server would be unable to find the email account.
In such cases, the email would fail to deliver to the recipient and would be bounced to the sender, with the error ‘550 5.1.1 : Recipient address rejected’.
Double-check the email address you’ve given in the email for spelling errors and confirm its a valid email account.
Also check that the domain is resolving to the correct server from your end and the routing is fine, using ‘dig’ and ‘trace route’ tools.
b. MX record for the recipient domain resolving to the wrong server
If the MX record for the recipient domain is resolving wrongly to some other remote server, then the email will not be routed to the correct mail server.
As a result, the mail server that received the mail will not be able to track the email account in it and hence mail delivery will fail. To confirm the MX records for a domain, use the command:
dig domain.com MX
DNS issues can also happen due to wrongly set DNS records such as wild card entries for the domain or priority for MX records set wrongly.
If any issues noted in the MX records for the recipient domain, contact the support for the server and get it sorted out. If the recipient server is yours, edit the DNS records and fix the issues.
In addition to the MX records, email routing within the server should also be checked. Verify that the emails are routed to the correct server and not any remote servers.
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c. Configuration settings in recipient mail server
Many recipient servers implement custom security settings in the mail server to avoid unwanted mails from abusing the server. Spam filters are major tools that block emails.
These security rules are implemented in the form of server-wide firewalls or domain-specific filters. A wrongly set email forwarder can also lead to incorrect email routing.
Certain ‘Message Delivery Restrictions’ for the recipient email account that may be blocking specific senders, can also end up giving error ‘550 5.1.1 : Recipient address rejected’.
To verify that the recipient server firewalls are not blocking your server, do:
telnet domain.com 25
If connectivity issues or email filters are blocking your emails, get the recipient domain filters and blacklists verified to rule out such blocks.
2. Issues with sender server
The 550 5.1.1 error can be caused due to issues at sender server too:
a. Sender is suspected for spamming
Many mail servers such as Postfix and Exchange have features to reject non-verifiable senders. Verifying senders can include checking SPF records to RDNS.
If the sender domain is in blacklist such as Spamhaus, the recipient mail server may reject mails from the server.
Verify that SPF records exist for the sender domain and RDNS is configured correctly. The command to verify RDNS is:
host IP address
Confirm that your server is not listed in any blacklists. If blacklisted, audit the server for any spamming scripts and secure the server against spammers.
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b. Sender email account hijacked
If there are numerous bounce messages noted in the mail logs, it can denote that someone is using the sender email account for spamming.
Even certain spamming scripts can send mass mails to different non-existing accounts, causing the logs to be filled with ‘550 5.1.1’ bounce errors.
Examine the email logs and confirm if any spamming is happening in the server.
Lock the suspicious email account without delay and change the password to a strong one. Audit the server for malicious scripts and implement strict password policy.
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c. Configuration issues in sender server
In rare cases, it has been noted that the recipient domain is configured as a local domain in the sender server. In such cases, domain would resolve incorrectly and email error happens.
Certain mail servers have outbound mail filtering configured in them, which can block the emails going out from it, and leading to email rejection messages.
Check email routing within the sender server by sending test mails and checking the logs for messages. Also verify that the outbound filter rules are not blocking the mails.
Today we discussed the various reasons for ‘550 5.5.1 : Recipient address rejected’ error and how to fix those.
Though this error is common in Exchange and Postfix, users who send to these servers may see the error, even if they are in other mail servers.
Since senders use email clients such as Outlook or Thunderbird to send mails, they will see the message in their email clients.
The other variant for the error ‘550 5.5.1 : Recipient address rejected’ are:
550 5.1.1 : The email account that you tried to reach does not exist 550 5.1.1 : User unknown 550 5.1.1 : Recipient address rejected: User unknown in virtual alias table 550 5.1.1 <firstname.lastname@example.org>: Recipient address rejected: User unknown in relay recipient table
Checking the email logs, configuring email clients and mail servers correctly, securing the servers against spamming and spoofing, etc. are crucial in email error debugging.
If you’d like to know how to secure your mail server and prevent email bounce errors, we’d be happy to talk to you.