Starting February 1, 2018, Oath (A Verizon company that owns both AOL and Yahoo!) began consolidating sending infrastructures between AOL and Yahoo!. This means that the AOL domains will continue to operate and accept email, but Yahoo! will handle spam filtering and processing.
You can get additional information about the changes and the impact here:
Because the process of consolidating infrastructures will take some time, some AOL domains may be handled by the old AOL infrastructure, while other AOL domains will be handled by the Yahoo! infrastructure. You can get additional information about troubleshooting for Yahoo! here:
You can check if the AOL domains you are sending to are handled by AOL or Yahoo! by entering the AOL domain with MX toolbox and performing an MX lookup. The results will display a Yahoo! hostname if it is being handled by Yahoo!. For example:
- aol.com: hostname = mx-aol.mail.gm0.yahoodns.net
- Ensure your reverse DNS (PTR) record for your IP address contains a fully qualified domain name. Make sure the PTR record does not use a generic domain such as in-addr.arpa. AOL will block email from IP addresses with a misconfigured reverse DNS record. Use a meaningful domain name such as: mail.yourdomain.com.
- Check if you send to a large number of unknown users. AOL prefers that you keep the number of unknown users to a minimum. If you have a high unknown user rate, it could be causing deliverability problems.
- Determine if all of your sending IP addresses are signed up on the AOL complaint feedback loop. Complaints are an important metric for determining your sending reputation at AOL. Be sure all complainers are added to a suppression list.
- Determine if your IP address is on a Blacklist. AOL uses the Spamhaus PBL blacklist in their filtering decisions. If your IP address is listed, refer to the blacklist listing criteria and fix the cause.
- Check your SMTP logs for clues regarding the issue. If your email is being throttled or blocked, check your SMTP logs for a response indicating a possible cause.
- Determine if your email authentication is working properly. A misconfigured SPF, DKIM or DMARC record can result in being filtered or blocked at AOL.
- Determine if your system sent an unexpected increase in volume. AOL may throttle your email when they see unexpected volume fluctuations.
- Reapply for whitelisting. AOL may remove your IP address from their internal whitelist without notice. If you are seeing throttling issues, check your IP reputation and reapply for whitelisting.
- Ensure that your sending system has not been compromised by a hacker and that all email coming from your system is authorized. AOL will block email from a compromised system. Ensure that your systems are not acting as an open relay or open proxy.
- In HTML messages, make sure all the links are transparent. Discrepancies between the apparent URL and the “real” URL of the destination site will trigger anti-phishing warnings. Don't use HTML code to make it look like the destination is a part of your domain.
- Check your connection and throughput settings and SMTP error logs to see if you are sending too much email to their servers. Reduce the settings if throttling occurs.
- Check your retry settings and increase time between retries if still experiencing throttling issues. You may want to limit the number of retries per message to 2 or 3 temporarily if needed until you can isolate a cause of the deliverability problems.