How we resolved the Hotmail deliverability Issue in CXM

How did we find out about it?

Some of our customers opened support tickets asking why emails were no longer being delivered to Hotmail mailboxes.
It’s easy to dismiss this as “just check the Junk folder” but actually, having emails consistently marked as spam and delivered to Junk folders can harm your email reputation and result in more “spam” verdicts (or worse - as we’ll cover later on).

Who did we contact about it?

Our emails are sent through a third-party service called Mailgun, who specialise in making sure emails get delivered without landing us on spammer lists. We used MXToolbox to help diagnose the issue and it appeared that the IP address we had been assigned had previously been blacklisted, MailChimp have a great article on how Blacklisting works. The image below shows the current status of that original IP. 

• We opened a support ticket with Mailgun, who assigned us a dedicated IP (one which no other service - not even other customers of Mailgun - can use) and we then assumed (wrongly) that the issues would magically be fixed.
• It’s important to note that it isn’t Mailgun’s fault these shared IPs get onto spammer blacklists - all it takes is one rogue consumer of the service to violate the terms of a given blacklist and all customers using the same IP will be affected.
• We then contacted “Outlook.com Deliverability Support” (also called “Sender Support”) using this form - after a small amount of email back-and-forth, we had some temporary mitigation put in place for our new dedicated IP, to improve its reputation while we sorted out the issues with poor/spammy content in our email templates.
• We opened support tickets with our customers to alert them to the potential Hotmail issues - and to schedule some changes in with them to the content of our email templates to improve their spam ratings.

What was the reason?

Ultimately, our deliverability issues came from multiple sources:

• The original shared outbound IP being on a blacklist - which potentially damaged the deliverability reputation of our customers’ domains (as used in their “From” email addresses).
• The new dedicated outbound IP having a bad reputation with Microsoft.
• The contents of our email templates - we ran these through a spam scorer called Melon Stork and we adjusted the wording of some of our email subjects as a result.

What steps have we taken to avoid this happening unnoticed again?

• We signed up for SNDS and JMRP with Microsoft using an @outlook.com account. With it, we can see stats on the percentage of our emails being marked as not being delivered - and their customers were able to contact them by phone. Having multiple channels of communication is important, to mitigate any problems you might have with any one of them. If you don’t have a support ticketing system, we recommend you invest in one soon, even if just to give your customers another route to contact you when emails are just not getting through.
• As we mentioned before, go here to set up SNDS and JMRP with Microsoft.
• Don’t rely on the response codes from Microsoft to verify whether your email was delivered or not. Almost all emails were being sent with a 250 OK response back from Hotmail, but some of those emails were either going to Junk or even not being delivered at all (this is a deliberate technique of Microsoft’s for content that is deemed as very spammy).
• Read Microsoft’s whitepaper on deliverability: - they mention the different criteria that can result in an email being dropped completely vs. being delivered to the Junk folder, among other useful tips.

Help! I need to sort this deliverability issue now!

Microsoft were very helpful when we contacted them - if you have an urgent deliverability problem, contact their “Sender support”. They might let you know that the IP has previously received special treatment (“mitigation” against spam verdicts) but after explaining the problem and our service in detail they were very accommodating. Note that it took several days (although this was over the weekend) for the mitigation they put in place to take effect, but their email responses were usually within just a couple of hours, which was very impressive for what is essentially a free service (to us). With their JMRP (Junk Mail Reporting Program) we can be sent copies of emails getting marked as spam, to help with further diagnosis.

In the interest of transparency, we proactively opened support tickets with each of our customers to alert them to the potential deliverability issues to Hotmail email addresses. This means they can be vigilant in future and would hopefully let us know quickly in the unlikely event that any of their customers weren’t receiving emails.

What steps should you take to help deliverability of your emails?

Remember that nothing 100% guarantees that your emails will be delivered to your users’ inboxes. Make sure your users can contact you in the event that they don’t (in our case, they were able to use our customer support solution, using Jadu CXM, to contact us despite emails not getting through).