There are some reasons why you have received a message with this error. We’ll dwell on the reasons, solutions and the ways to avoid this nasty error.

The 550 5.1.1 error

Reasons of the 550 5.1.1 error:

  • Invalid email address. You may have an invalid recipient’s address, it means that it was active at the moment you got it, but now it no longer exists, that’s why your email can’t be delivered.
  • Typos in the email address. Any mistake, even a missing character can lead your email sending to a failure, since there is no such address.
  • Misconfiguration. Any bug or misconfiguration of the recipient’s server may prevent them from getting your email.
  • Outdated DNS record. DNS settings may be not correct for the recipient’s domain, that’s why MX can’t resolve correctly.

How to get rid of the 550 5.1.1 error?

  • Make sure there are no spelling mistakes in the recipient’s email address and check if it is still valid. There are a lot of tools on the Internet for this purpose. Make use of them!
  • Your DNS record is outdated and the recipient’s server can’t resolve it. Update it! You can use DNS Lookup to get to know if there are any problems.
  • Still, having checked the email address validity, you see that everything is alright, but you continue receiving the 550 5.1.1 error message. In this case, contact the email address owner and inform on possible problems with the mail server configuration settings, stating that you have done everything from your side.

How to avoid the 550 5.1.1 error message while sending bulk email campaigns?

If you regularly send bulk email campaigns to a large number of recipients, you may receive a message with this error with the same frequency and this is quite reasonable. If you send emails to invalid email addresses, it means that you don’t know who you are sending to. Thus, email providers consider your emails to be spam and, as a result, you receive the 550 5.1.1 error message. Moreover, today it is easy to get a great plenty of email addresses, using special software like “harvesters” or “harvesting bots”. So, providers are partially right. But, to avoid this problem, make a habit of regular checking the email addresses you have to keep your mailing lists clean.

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
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