When sending email, it may happen that you get a bounce message with code 550-5.7.1. This error message is almost always the result of a misconfiguration, which causes the message to be stopped as possible spam.

In this article, we show some of the more common 550-5.7.1 messages and explain how to solve them. Below is an overview of examples of error messages which are discussed in this article:

• Our system has detected that this message is likely unsolicited mail (SPAM). To reduce the amount of spam, this message has been blocked. (12zGg44vPFz5Bcw7)
   
• This message does not have authentication information or fails to pass authentication checks. To best protect our users from spam, the message has been blocked.
   
• Our system has detected that this message does not meet IPv6 sending guidelines regarding PTR records and 550-5.7.1 authentication.(VPS)
   
• Unfortunately, messages from [123.123.123.123] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).(VPS)

2019-02-02 09:00:00 SERVER -> CLIENT: 550 5.7.1 Our system has detected that this message is likely unsolicited mail (SPAM). To reduce the amount of spam, this message has been blocked. (12zGg44vPFz5Bcw7)

We perform a check on mail sent via our servers (i.e., if you use a web hosting package or the VPS mail service) to see if that mail could be classified as spam. We do this to prevent, for example, an infected website sending a lot of spam and our mail servers getting a negative IP reputation as a result, which would cause mail from all our customers to get send with more difficulty. 

If you get this message, it means that our spam check has stopped your message as possible spam. Some of the more common causes that you yourself can exclude are:

• An incorrectly set SPF record. In our article on SPF records, we explain how to set up SPF records.
• An incorrectly set DKIM record. In our article on DKIM records, we explain how to set a DKIM record in general. In our article on the VPS mail service, we explain how this works if you use a VPS with our mail service.
• A web form in which the sender and receiver are identical. For example, this often happens with forms on WordPress websites: they usually forward messages from people. This means that even if someone fills in your form with, for example, an @hotmail.com address, your message will be forwarded from, for example, info@example.com to info@example.com. In this case, it is better to use a separate address for your form, for example form@example.com which forwards to info@example.com. 
• Your mail address in on a spam list. You can check this for most spam lists on this website.

In other cases, the formatting of the mail headers is often incorrect. This is usually the result of incorrectly constructed code, for example, in a website plugin, or PHP script. Only its creator can solve the problem. Our support department can check for you whether this is indeed the case. 

Message has been blocked. Please visit 550-5.7.1 host aspmx.l.google.com[2a00:1450:4013:c03::1b] said: 550-5.7.1 This message does not have authentication information or fails to pass 550-5.7.1 authentication checks. To best protect our users from spam, the 550-5.7.1 https://support.google.com/mail/answer/81126#authentication for more 550 5.7.1 information.

This message is almost always the result of an incorrectly set SPF record. In our article on SPF records, we explain how to set up SPF records. It is important that if you do not use our nameservers, you set the SPF record with the party of whom you use the nameservers.

SMTP error from remote mail server after end of data: host gmail-smtp-in.l.google.com [2a00:1450:4013:c01::1b]: 550-5.7.1 [2a01:7c8:aab1:111::1] Our system has detected that this message does 550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and 550-5.7.1 authentication. Please review 550-5.7.1 https://support.google.com/mail/?p=IPv6AuthError for more information 550 5.7.1 . v27si349922ejg.227 - gsmtp

We only encounter this error with VPSs and means that the reverse DNS for the VPS is set incorrectly. In our article on reverse-DNS, we explain how to set this correctly.

host outlook-com.olc.protection.outlook.com [104.47.6.33] SMTP error from remote mail server after pipelined MAIL FROM:<mail@example.com> SIZE=17661: 550 5.7.1 Unfortunately, messages from [123.123.123.123] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors." [VE1EUR02FT016.eop-EUR02.prod.protection.outlook.com]

We only encounter this error with VPSs and means that Microsoft is blocking the IP address of your VPS. This can happen, for example, if several people have marked mail sent from your VPS as spam, or you send newsletters without an unsubscribe option. In this article, we explain how you can apply for a delisting.

Should you have any questions left regarding this article, do not hesitate to contact our support department. You can reach them via the ‘ContactUs’ button at the bottom of this page.

If you want to discuss this article with other users, or if you encounter another 550 5.7.1 error about which you want information, please leave a message under 'Comments'.