AOL Rejecting email sent via PHP mail (error 5.2.1)

Question

Recently AOL has started rejecting emails sent from my production server.

Customers make product enquiries through my site and can "cc" themselves if they wish. I check for spam (e.g. don't send if request contains banned phrases, urls, etc). However, recently, if the enquirer is an AOL customer, the message bounces:

<*removed!*@aol.com>: host mailin-04.mx.aol.com[64.12.88.132] said: 521 5.2.1 :
    AOL will not accept delivery of this message. (in reply to end of DATA
    command)

Email protocol is not my area of expertise! I just use the standard PHP mail() function and this has worked ok for years.

I have looked through the AOL Postmaster support pages and contacted AOL (which, obviously, was my first port of call - but they have yet to respond), plus I don't really understand the problem (which is 50% of finding the solution!).

http://postmaster-blog.aol.com/2014/04/22/aol-mail-updates-dmarc-policy-to-reject/

...it seems as though AOL are saying "we don't like the way that you send emails, sorry to inconvenience you..."

If anyone has any experience or specific insight into how to get AOL to accept emails then I would love to hear from you. I'm guessing that it could be something to do with how my emails are formed: this hasn't changed in years and (previously) I've had no reason to look at the code:

Here is an edited version of how I send emails...

$recipient = "\"$supplier[supplierName]\" <$supplier[supplierEmail]>";
$subject = "$supplier[supplierName] enquiry";
$headers = "MIME-Version: 1.0".PHP_EOL ;
$headers .= "Content-type: text/html; charset=utf-8".PHP_EOL;
$headers .= "Reply-To: \"$cleanArrayEmail[realname]\" <$cleanArrayEmail[email]>".PHP_EOL;
$headers .= "From: \"Admin\" <ADMIN_EMAIL>".PHP_EOL;
if ($_POST['cc']){$headers .= "cc: \"$cleanArrayEmail[realname]\" <$cleanArrayEmail[email]>".PHP_EOL;}

mail ($recipient, $subject, $msg, $headers, '-f'. ADMIN_EMAIL );

Many thanks Steve

Answer 1

AOL recently implemented DMARC Rejection, as did Yahoo before them. What this means is that if your PHP code attempts to send an email that claims to be FROM a Yahoo.com or AOL.com address, it will not be accepted by the recipients mail server, be it AOL, Yahoo, Gmail, or anyone else that supports DMARC.

Look at your email FROM address, is it AOL or Yahoo? If so then DMARC may be your problem, if not than it's probably something else. DMARC policies are set in DNS records for every domain, you can use this tool to check the DMARC policy for your FROM domain.

https://dmarcian.com/dmarc-inspector/aol.com

Answer 2

To the best of my knowledge, AOL indeed rejects mails, which either claim to be from AOL (FROM header, DMARC), or mails, which are not from AOL, but use an AOL address as Reply-To header. However, I cannot say whether this is due DMARC or not. I hence can confirm what Steve is saying, I noticed the same behavior in my application.

As soon as the Reply-To header is removed or changed to a non-AOL address, the mail is delivered correctly. It is however interesting to note, that only the AOL customer which is put in the Reply-To field does not receive the mail. If there are other AOL-mails in the TO header, those delivered and not blocked.

I mentioned that I am not sure, whether they reject it due to DMARC or not. An interesting hint can be found at the AOL postmaster blog introducing DMARC. Here it is explicitly recommended to use the Reply-To line and put the actual address in there. Further, mails rejected to a failed DMARC check are normally rejected using an error code noting the failed DMARC check.

Answer 3

Ditto what waza-ari said (AOL will not deliver email that is sent from a non-AOL server with a Reply-to containing an AOL address) - and this also applies to addresses containing a Compuserve address. I have heard it also applies to Hotmail & Yahoo addresses, but have not personally experienced that.

I have system code that emails 2 people if one of them accesses the other's research data (it's a collaborative research system, so users want to know if another person shares their interests). I prefer to have the Reply-to contain only their two addresses, as I don't need to be part of the subsequent conversation. However, I can't put an AOL/Compuserve address in the Reply-to field, as it will be rejected.

My solution is for the code to parse the user addresses and if either is in one of those domains, it substitutes our site's "info@" address as the Reply-to address, and the body of the email shows both user's addresses and tells them to email each other. This might not scale well to a larger customer base of users who ignore instructions and just hit Reply. It works well for me, but I probably generate less than 100 of these emails per month, and in a year of using this code, I've never had someone accidentally reply to me. I use the same "parse and substitute" code in our contact form where a user's email address would normally be inserted as the Reply-to.