php - e-mails send to microsoft addresses end up in spam, others are fine

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For a webshop we are sending e-mails to our customers for status information about the order. On a daily basis, we send around 4000 e-mails.

These e-mails are send with PHPMailer (5.2.14 | Current latest). We have setup SPF and DKIM and those are fine. Tested them with several tools. Also we get a SpamAssassin score of 0.1.

When we send an e-mail to a @gmail.com user, everything is fine, the e-mail is put in the inbox. But when we send exact the same e-mail to a Microsoft user, @hotmail.com / @live.com / @outlook.com / @msn.com, this e-mail ends up in the SPAM folder.

We only have issues with Microsoft accounts.

It's driving me crazy, I don't know what to do next.
Customers are calling us about the fact that they don't get any e-mails. Some even say that the e-mail is also not in the SPAM folder.

I know this is a very open question, I hope we can get a discussion on what to do next. I have been looking at the internet for all kinds of things, but didn't find the right thing yet.

We also setup DMARC, but to be honest, it seems quite difficult to me.

932

Answer

Solution:

Generally, large email providers in recent years started to offer Postmaster tools to help determining why email get in spam or rejected (but targeting ISPs, not end users).

Microsoft calls this Smart Network Data Service (SNDS) where an ISP can determine and follow IP or domain reputation.

Along with SPF and DKIM you already have installed you're advised to configure DMARC for aggregate (or else) reports since it may help you to be informed about actual problems within your domain.

And it usually boils down to having bad reputation (for your IP, your domain), which sometimes can be lifted by requesting, and sometimes it expires in a few days unless your system keeps doing bad things; or sometimes a weird filter disliking your actual content (and since a normal plain text email would deliver you can use trial-and-error to determine which part is disliked).

People are also looking for solutions to the problem: regex - How to regex_replace that with PHP?

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