AOL mail - blocking Discourse emails?

I know many you here have your Discourse mail being sent via Mandrill

Are any of you seeing addresses bouncing mail more frequently?

Obviously you will only get the bounce email notification if you have configured an email address to receive these bounce emails under Forward Bounce Notifications To This Address. But you can see both soft, hard bounces and rejected in your Mandrill outbound activity page.

I’m seeing AOL will not accept delivery of this message.

After talking to one user (a forum moderator) he found that Discourse emails were indeed ending up in SPAM - after asking him to flag them as “NOT SPAM” and removing his email address from the Rejection Blacklist emails were accepted again…

So far this has happened for 4 separate accounts - and just got me wondering if anybody else had seen the same?

The email notifications sent to these addresses would have derived from absolutely clean non-spammy posts containing interesting English content (at least to a human).

I do have “Track Opens” and “Track Clicks (HTML only)” enabled and add Google Analytics Tracking to links and include Auto-Submitted: auto-generated as per RFC3834.


Hello, this is the mail server on

I am sending you this message to inform you on the delivery status of a
message you previously sent.  Immediately below you will find a list of
the affected recipients;  also attached is a Delivery Status Notification
(DSN) report in standard format, as well as the headers of the original

  <>  delivery failed; will not continue trying

Final-Recipient: rfc822;
Action: failed
Status: 5.0.0 (undefined status)
Remote-MTA: dns; (
Diagnostic-Code: smtp;521 5.2.1 : AOL will not accept delivery of this message.
X-PowerMTA-BounceCategory: other

Are you fully set up with DKIM and all those good deliverability things in Mandrill?


Another plug for the excellent which @watchmanmonitor turned me on to!


So I picked this topic up with Mandrill Support and with their permission I’ll post Jonathan’s relevant responses here in their entirety for your reference:

Jonathan (Mandrill Support)
May 7, 3:15 PM

Hey Dean,

Thanks for reaching out and providing those details. You’re absolutely right about AOL either deferring or outright bouncing some of your emails, which is also being reported by other users. While there isn’t too much information available to us about the source of the issue, I can confirm that this isn’t due to any issue on Mandrill’s end, and those bounces aren’t due to any blacklisting. Instead, it appears to be a more endemic issue on the receiving end that’s affecting emails sent to AOL from multiple platforms.

It’s also worth noting that the provided blacklist fortunately isn’t one we’d view as particularly reputable, and it’s unlikely to be used by major ISPs like AOL. When it comes to blacklists, we’d generally advise focusing on the largest, most reputable blacklist services—namely SpamCop—unless you’re specifically seeing emails blocked because of the listing.

We’re also actively trying to investigate this particular issue with AOL, but I unfortunately wouldn’t be able to provide a timeframe for when things might improve. However, definitely feel free to let us know if there are any questions, and we’ll be glad to help.

After requesting permission to post his response:

Jonathan (Mandrill Support)
May 7, 4:04 PM

Hey Dean,

No problem. You’re also welcome to convey this information to other users, but it may be worthwhile to include some caveats, particularly since this type of rejection is unfortunately vague and may cause confusion if the same diagnostic code is provided in the future for an unrelated issue.

However, I think it’s at least fine to mention in the forum that other users are reporting the issue, and that we’re confident it’s not an issue on Mandrill’s end or due to any blacklisting, possibly while referencing that the post is specifically in regards to bounces and deferrals that are occurring this week with the following SMTP replies (as AOL has other diagnostic codes, too):

521 5.2.1 : AOL will not accept delivery of this message.
421 4.2.1 "Service unavailable. Please try again later."
That’s should hopefully help avoid any confusion that might be caused by someone stumbling across the issue in the future and simply seeing my last message provided there.

I also wanted to add that Spamhaus is a particularly reputable and influential blacklist, as I noticed I forgot to mention them, previously. This article from MailChimp also does a nice job of explaining the differences between different blacklists, while listing a few other important ones:

I hope that information helps.


I got a notification at work today from our corporate folks:

From: XXXXXX Security Alerts 
Sent: Thursday, May 07, 2015 13:45
Subject: Outage Notification -
Good Afternoon,
We are currently experiencing issues sending email to  The Windows Team is currently working with AOL to resolve these issues and will update once it has been resolved.
Thank you,
XXXXXX Support Center

Same issue here. I hope it gets sorted soon.

@DeanMarkTaylor was there ever any resolution on this issue?

1 Like

Sorry to say I had no further response.

I later transferred to SparkPost as a mail provider where mail deliverablity on the shared IP was a different issue where there more of a problem dependably with delivering to Microsoft domains (“hotmail” etc.)

Moving to a dedicated IP reduced these issues.

However a combination of:

  1. so much time passing (years) the number of users with a “AOL” address reduced super low percentage
  2. number of errors became so low

It became unimportant.