Hotmail / Yahoo (Others?) blocking email notifications?

Question

I've got a website (currently in development for a third party, I'm sorry I can't show) that requires users to confirm their contact information by, clicking on a link sent to their email address, upon registration for the website. It's a pretty standard practice, not very technical or unique, which is why I was surprised to find that Hotmail and Yahoo (and maybe others, I'm not sure) are blocking any email messages that are generated dynamically via the PHP code that runs the website. I'm using the PHP framework CodeIgniter, and making use of their email library. I've checked my code and everything looks great, and I've also looked over the email class and it looks tip-top as well. Not to mention, the message sent are delivered to every other mail service I've tried, including gmail, and several POP accounts. This leads me to believe that the problem is on the Hotmail/Yahoo end. I suspect they are purposefully rejecting/bouncing the message due to formatting, subject content, or some other arbitrary issue. The HTML email design is minimal, only really utilizing HTML for header tags a link. The subject of the message simply states "Welcome to __", and is addressed from "support@____.com".

My question is, are there any articles relating to what could be causing this that I could read to better understand why the messages are being rejected, so I can fix the issue? Preferrably the article or document would be from Hotmail and Yahoo (with inside info), or from somebody who has experienced the same issue, and has come to a solution. Also, are there any available utilities to test what is actually happening with the message once it hits their servers (i.e. Is it being bounced, or something else?)

Thank you very much! :)

Answer 1

My friend had a notification system that he has his PHP code send the notifications using a SMTP. So his notiifications were really sent from his Gmail account. He did this to prevent hotmail/etc from auto blocking the emails.

I don't know if this helps

Answer 2

Make sure you have SPF records for your domain, and that they are set correctly. This will go a long way.

Email deliverability is a complex topic. At a previous gig, I was a member of the ESPC. This PDF link may be helpful, or outdated. Also see this other similar SO question.

Answer 3

What headers are yous ending along with your e-mail? Does it contain enough "valueable text" within the e-mail, or is it mostly links (to your site, the confirmation link, the "contact us"-link, ...). This can play a big part in spamfilters a like, to determine whether an e-mail contains original and valueable content.

Answer 4

I'm having similar problems - only with hotmail.com. Gmail, and local national providers work OK. My mail is combined as such:

 $headers  = "MIME-Version: 1.0\r\n";
 $headers .= "Content-type: text/plain; charset=iso-8859-1\r\n";
 $headers .= "X-Priority: 1\r\n";
 $headers .= "X-MSMail-Priority: High\r\n";
 $headers .= "X-Mailer: Company name\r\n";
 $headers .= "From: \"Company name\" <[email protected]>";
 mail($email, "title", $message, $headers,"[email protected]");

All suggestions welcome