Mail.ru built most of its spam filter technology in-house and created its own proprietary bayesian heuristics filters. Mail.ru also has a robust reputation filter that looks at different reputation metrics such as complaints, unknown users, spam traps and engagement. Any sender with a negative sending reputation may be blocked from sending messages to Mail.Ru. Many senders have deliverability success at Mail.ru by following their best practice guidelines.
- Check your domain statistics using Mail.ru’s sender statistics program. This is a useful tool for helping you investigate problem areas. You will be required to verify you own the domain as part of the signup process.
- Determine if you are you using confirmed opt-in (COI) consent for all Mail.ru subscribers. Failure to use COI is one of the top reasons Mail.ru blocks senders.
- Determine if all of your sending IP addresses are signed up on the Mail.ru complaint feedback loop and that complainers are being immediately supressed from all future messages.
- Check your SMTP error codes for clues on deliverability problems. Mail.ru does not publish a list of error codes, but they may include a short message and link in the error message to aid you in your traoubleshooting efforts.
- If your SMTP error codes indicate your IP is on their internal blacklist, investigate and fix all issues and then request removal.
- Check if your IP address is listed on the following blacklists as well. Investigate and fix any issues if your IP addresses are listed.
- Spamhaus: Spamhaus will give you further direction if your IP address is listed.
- Return Path Reputation Network Blacklist lookup
- Return Path Reputation Network Blacklist removal request
- Scan your systems to ensure you are not hosting or sending viruses or content with links to websites known for distributing malware.
- Check Kaspersky to see if your IP address is part of the Simda botnet. If your IP address is listed, your system may be infected with malware and spyware. Mail.ru uses Kaspersky for virus and malware detection.
- Ensure your system is not configured as an open relay or open proxy. Mail.ru will block your IP address if it is being used to distribute spam by an unauthorized third party.