If you encounter an Error 550 Message Rejected or blocked while attempting to send an email, it indicates that a spam filter has prevented the message from being sent. The reason for this issue is that your email domain has been listed in a Real-time Blackhole List (RBL). To resolve this problem, you will need to take measures to have your email domain whitelisted as non-spam.
How to check if your email is blacklisted?
You can use tools like MXToolbox to see if your email is blacklisted. In order to check that use your email domain, part comes after @ in MXToolbox. MXToolbox checks your email domain against over 100 blacklists.
If it is blacklisted, you must contact blacklist to request for delisting. Please note that delisting may take some time.
How do I Prevent my email domain from being blacklisted?
Don’t send spam. Instead of blaming Blacklists for deliverability problems, verify what messages you are sending in the first place. This doesn’t just apply to your design of mailings. Check your logs carefully – it is possible that an unauthorized mailing has taken place via your account or IP address, which led to the listings.
Configure security protocols such as SPF, DKIM, and DMARC. Adding appropriate DNS entries protects senders from having their sending domains impersonated by potential spammers, who often use unprotected domains to conduct phishing.
Keep track of your email statistics – if you notice that emails are not being opened, ‘give a rest’ to recipients who are not interested in your messages. Send another engaging email, e.g. with an interesting, personalized offer, only after some time. Otherwise, you increase the chances that the recipient will mark your message as SPAM. Engagement is one of the key factors when it comes to good deliverability and reputation, so be sure to segment your contact base appropriately and only send emails to the group that can expect the content.
Never buy a contact database. First – the lack of proper approvals is not compliant with GDPR, second – this type of contact group is very often outdated and contains addresses that do not exist (thus increasing the number of Hard bounce statuses). Old databases may also contain spam trap addresses.
Respond to abuse reports. Set up an Abuse mailbox for this purpose, to which Blacklist Administrators can send reports of observed abuse attempts, and recipients themselves – objections to receiving unwanted mail.
Do not send large messages. According to good practice, emails should not exceed 15 MB – larger emails may appear suspicious and automatically redirected to the SPAM folder. Also, ensure that attachments are virus-free and do not contain malware.
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