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As its name goes the spam 550 error refers to a condition where the email which you send is not accepted by the recipient’s server. As a default setting, the recipient’s server relays an automatic message to the sender which reads “550: High probability of spam”. This condition is also sometimes called bouncing. Spam filters employ these mechanisms to protect their users from potential hazardous emails which might lead to the foundation of fraud and various other cyber crimes. As daunting as this all sounds, there are tried and tested ways in which you can make sure that your email is not wrongly categorized as spam. That being said, it is almost impossible to run a completely bounceless non-targeted campaign because we don’t have the information about how all the different email servers are configured.

Following is a comprehensive list of causes that may be behind you getting a 550 error:

1. The integrity of your origin email address is compromised as is flagged by the recipient’s server.
2. Your domain has been blocked (possible reasons: payment of dues, expiration or subscription, etc.).
3. Your own internet server has identified the outgoing email as spam and therefore has flagged it. 
4. The destination email address does not exist.
5. The destination email address is currently unavailable and/or suspended.
6. Unavailability of the recipient’s hosting server.
7. Your email is mistakenly identified as spam by the recipient’s email server.
8. The destination email server failed to identify your email address.

Here are some common phrases that you can use to identify that you have received a 550 error:

1. Email Error 550 5.1.0 Address Rejected means that the recipient’s server is voluntarily refusing to accept emails from you. One possible reason for this could be that you have been blocked by the person who you are trying to send an email to.
2. Email Error 550 5.1.1 suggests that the email address which you had entered as destination is inavlid or doesn’t exist in the required domain.
3. Email Error 550 Denied by Policy means that the recipient’s internal security mechanisms have blocked outbound emails, mostly to prevent attackers from launching brute force attacks against their server.
4. Email Error 550 5.4.1 means that the recipient’s server doesn’t accept emails from the domain which you are using. This is usually the case if you are using blacklisted domains or IP addresses.
5. Email Error 550 5.7.0 Message Size Violation suggests that you have exceeded the file size which is allowed in your email.
6. Email Error 550 5.7.1 Access Denied means that your email was rejected by the security policies on the recipient’s side or wrongly by misconfiguration of DNS.
7. Email Error 550 Administrative Prohibition can mean any of the following things - you are using blacklisted domains, recipient’s domain is blacklisted, SMTP server has dynamic IP.
8. Email Error 550 Relay Not Permitted means that your server no longer has email sending privileges.
9. Email Error 550 Quarantined / 550 Error Recipient Quarantined means that your email address was flagged as spam.
10. Email Error 550 SPF occurs when the IP which you are using to send the email from is not recorded in the Sender Policy Framework (SPF) which leads to your email failing some verification steps.
11. Email Error 550 Reverse DNS means that there is an absence of reverse DNS of sender’s IP address and there is a mismatch of records present in the domain.
12. Email Error 550 Recipient Unknown happens when your server is unable to find the destination account. Most prominent reason behind this includes typos.
13. Email Error 550 Host Unknown occurs when your specified hostname is non-existent/ incorrect.
14. Email Error 550 Authentication is required for relay means that the SMTP authentication is missing which is required to send outbound emails.
15. Server Error 550/ 550 Blocked Error happens when the email that you are trying to send has been blocked by the recipient’s server.
16. Error 550 #5.1.0 Address Rejected indicates that the recipient’s server has refused to accept the email from your address. This could happen due to the origin email address being blocked by the destination servers.
17. Server Error 550 This Domain is Not Hosted Here occurs when the recipient’s username is not accessible to the sender’s server. Other reasons for the same error include typing errors in the emails and incorrect MX records which direct to the wrong server.
18. Error 550 in Outlook suggests that 550 authentication is required for relay. In simple words, it means that your SMTP server is yet to be authenticated to send out emails.

Now that we’ve talked about the potential causes and common phrases associated with 550 Spam errors, let us now look at some ways using which we can minimize the 550 errors from our campaigns.

Sending Limit:

It is a good practice to enforce a daily outgoing limit on your IP addresses. If the number of emails sent per day from a particular domain or IP exceeds the humanely accepted value by various spam filters across the internet then your domain is very vulnerable to being blacklisted. If you are sending too many emails then your activities may be associated with the activities of a spammer by the governing technologies. Many service providers have a very strict limit in this regard and you should always aim to finish your daily campaigns well within that maxima.

Curate your Content:

There is a certain way in which spam emails are created. This is so that the most vulnerable are easily convinced. Over time, spam filters have become accustomed to the kind of language that is used in spam emails. This should be comprehensively understood by every email marketer because one one hand iit means that fewer spam emails enter inboxes giving more room for genuine emails but also any outbound email that matches the language of a spam email will be immediately flagged. This is one of the most common causes behind many 550 errors and it can result in your healthy IP getting blacklisted. There are various words that can trigger a particular spam filter. We highly recommend making sure that these words do not make their way into your email. So, to reduce your 550 Errors, it is important to curate your email content so that it is genuine and void of anything that could trigger spam filters.

DNS Setup:

This is a sure shot way of making sure that everything is perfect for your campaigns from the technical side. The DNS (Domain Name System) basically governs every protocol that exists on the internet. So, to avoid 550 Spam errors, it is highly recommended to build and verify proper security and transactional protocols such as SPF (Sender Policy Framework), DKIM (Domain Keys Identified Mail), DMARC (Domain-based Message Authentication Reporting and Conformance) under your DNS.      

Changing Domain

Change the domain name when you read error messages such as “low reputation of sending domain”. Using multiple domains to send emails to different ISPs (G Suite, Outlook, yahoo, etc.) can yield quick results.

Contact us to know more techniques on solving 550 and 553 errors while sending cold emails or doing bulk emailing.