Note: SMTP error codes are not an exact science, because different servers can assign different meanings to the same error code. However, there are things that are likely to be true, and we are going to talk about them.
You are reading this because you’ve received an automated message with a “550 5.1.1” error code in it. There are couple of things that could have caused this error:
- The recipient address does not exist: you may possess an outdated email that was valid at one time.
- There are typos in the recipient’s email address, which means that the address to which you are trying to send the email has never existed.
- If your MX record was changed, you may have an outdated DNS record and you were trying to resolve your MX record to an IP that no longer hosted it.
- There is something wrong with the configuration of the receiving server.
How you can fix the 550 5.1.1 error
- Check the email for typos (sometimes they are quite obvious, for example: firstname.lastname@example.org) and verify it. You can use an online tool that serves this purpose—there are lots of them on the Internet.
- Your DNS record is stale and cannot be resolved by the recipient server. It needs to be updated. Perform DNS lookup for your domain (DNS Lookup) and push the "Find problems" button. Consult the webmaster if you see any errors in the resulting list.
- If everything looks okay, or you get the same error when trying to send the email again, even though you are sure that the address exists and is typed correctly, you should find another way to contact the owner of the email and let them know that there is something wrong with the mailserver configuration on their side—there is nothing you can do about it yourself.
Avoiding the 550 5.1.1 error when working with bulk email lists
If you send newsletters or a large group of emails to a list of recipients, you may receive big quantities of emails with the “550 5.1.1” code. A certain number of these “bounce” emails signals email hosting providers about the possibility that the client is sending spam to unverified email addresses.
The logic behind this is the following: if you don’t know if an email address exists, there is a good chance you don’t know anything about the recipient, and that the email may have been obtained by email scraping (or email harvesting), which is a common behavior among spammers.
If we assume that you are indeed an email marketer or just a person who has to send large quantities of emails on regular basis, you simply have to add email verification to your routine. If we’re talking thousands of emails, you have to automate the process somehow. That’s where a bulk email verifier comes into play.
The most common 550 5.5.1 messages
- 550 5.1.1 : The email account that you tried to reach does not exist
- 550 5.1.1 : Recipient rejected
- 550 5.1.1 : User unknown
- 550 5.1.1 : Recipient address rejected: User unknown in virtual alias table
The 554 5.7.1 SMTP error