In this blog post we will talk about the most common error “550 permanent failure for one or more recipients”. This SMTP (Simple Mail Transfer Protocol) error occurs when the recipient mail server blocks email. There are various reasons for this such as restrictions, blacklisted IP addresses, bad DNS records, etc. We cannot know what the exact issue is. Therefore, we need to investigate to confirm if it is related to the sender’s or the recipient’s mail server. In the next paragraph, we will explain what steps need to be taken to detect what makes this issue appear.
First we will talk about the issues related to the SENDER’S EMAIL SERVER. Let’s get started!
Check the DNS records
By DNS records we mean the SPF, DKIM, and DMARC txt records in your DNS zone. You have to have all these valid records if you want your email not to be blocked by recipient servers.
SPF: The SPF (Sender Policy Framework) is a type of TXT record that defines the mail server domains that are allowed to send email on behalf of your domain. It lists all the servers authorized to send emails from a particular domain. If you do not have a valid SPF record for your domain the recipient server will immediately block the email. This is done since there is no authorized server for that domain.
DKIM: The DKIM (Domain Key Identified Mail) is an email authentication method that uses a digital signature to let the receiver of an email know that the message was sent and authorized by the owner of the domain. The DKIM helps prevent the spammers and other malicious scripts from impersonating the information from a legitimate domain.
DMARC: The DMARC (Domain-based Message Authentication Reporting and Conformance) record is a TXT record that tells the receiving mail server what to do after the checks for SPF and DKIM records. If there is no DMARC record, the email will get through even without valid SPF and DKIM records.
Check the Email Address of the receiver
This step is very easy, but sometimes is worth checking twice. Typically this is because you might have just input the recipient’s email address incorrectly. Check if that email address exist before you try to send the mail. You can use some online free checker tools by typing “email validator checker” on Google.
Blacklisted server IP address
Your server IP address might be blacklisted due to various reasons. If the IP is blacklisted you will not be able to send emails. Email servers work with third-party companies maintaining an IP address database of high volume emails senders and periodically block them. If your server IP address is in these databases the receiver mail server will block all sent emails. To prevent this, you need to check if your server IP address is listed and send a blacklist removal request. You will need to provide your domain name and the reason your IP address should not be on the list.
Check for Malicious Scripts
Running a malware scan would be helpful if there are malicious scripts uploaded on your server. Those malicious scripts can get into the email settings and send too many emails in a short period. This may lead your IP address to be blocked.
The recipient MX record
If the recipient MX record is not valid than the recipient server will not be able to receive an email. The MX record can be checked with some free online DNS checker tools.
In the rest paragraphs we will talk about the issues related to the RECEIVER’S EMAIL SERVER. Let’s say that we are the owner of the receiver email server. We can debug the issue on the other side as well.
Check the Firewall
Review your Firewall rules and if the IP address of the sending server is blocked, unblock it.
Check the SPAM Threshold
The SPAM threshold is the percentage of emails sent to a number of those emails marked as spam. For example, if you send 1000 emails and 1 is marked spam, you have a 0.1% spam threshold. A lower spam threshold score, such as a one, is aggressive. This labels many messages as spam, including messages that may not be spam. However, a higher value, such as a ten, is passive and only labels messages that are spam.
Check the Mailbox
When the recipient’s email inbox is full, it cannot accept any more emails, and the mail server rejects incoming messages. This will lead to a 550 error for one or more recipients. The solution is to increase the mailbox quota or remove some unnecessary emails to free up some disk space.
Conclusion
These were the basic steps to check whether the issue is on the sender’s or the recipient’s side. If you want to make marketing campaigns, and host email marketing business software, you can use some mass mailing services like Mailgun, Sendgrid, etc, to send emails. This way your VPS server won’t be blocked, since this software is made for sending a huge amount of emails.
That’s it. You successfully learned about the 550 Permanent Failure for on or more Recipients issue and how to fix it.
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