Got a call from a long-time client last week. They run a pretty successful WooCommerce store, and their order confirmation emails were landing in spam. Or worse, not arriving at all. They were getting angry support tickets from customers who thought their orders had vanished into thin air. A total mess. It’s the kind of thing that kills trust in a business, fast. My initial thought was, “Okay, classic WordPress email reliability problem.”
My first move? Set them up with a proper SMTP service. It’s the standard play. Usually, that cleans things up. But even after routing everything through a transactional email provider, a small but significant number of emails were still getting flagged by aggressive spam filters. Here’s the kicker: the root of the problem wasn’t just the server, it was deeper. It was in the guts of WordPress itself.
How WordPress 6.9 Improves Email Reliability
For years, developers like me have had to wrestle with the quirks of the wp_mail() function. It’s a core part of WordPress, but it’s had some long-standing issues that often require workarounds. Thankfully, as detailed in the official WordPress Core dev notes, the upcoming release of WordPress 6.9 finally addresses some of these headaches directly. No more band-aids. For a full breakdown you can check the source at make.wordpress.org, but here’s the practical version.
1. The Sender Address Mismatch
This was my client’s biggest issue. A lot of mail servers, when they send an email from WordPress, set the “sender address” (or Return-Path) to something generic, like www-data@hostgator-node123.com. Even if your “From” address was orders@mycoolshop.com, spam filters would see the mismatch and flag it. Shady. WordPress 6.9 will now intelligently set the sender address to match your “From” header. It’s a small change that makes a huge difference for deliverability.
If you have a more complex setup, like sending emails from a subdomain, you might still need to tweak it. But for 90% of sites, this just works out of the box. You might even find your old SMTP plugin has less work to do.
2. Fixing Corrupted Characters
Ever seen an email with a bunch of garbled characters like â€" instead of a simple dash? This could happen because the underlying PHPMailer object WordPress uses would sometimes “remember” the encoding from a previous email in the same request. If you sent a plain-text email and then a complex HTML one right after, the second one could get messed up. WordPress 6.9 now resets the encoding for every single email, ensuring each one is sent correctly based on its own content. Simple. Clean.
3. The 17-Year-Old Multipart Bug
This one is a deep cut. For the better part of two decades, there was a bug in how WordPress handled multipart messages—emails that have both an HTML and a plain-text version. In certain edge cases, WordPress would send a corrupted Content-Type header, which could break the email entirely. The fix in 6.9 simplifies the logic and lets the underlying PHPMailer library handle it correctly. And that was it. A 17-year-old bug, squashed.
What This Means for You
For most site owners, WordPress 6.9 means your emails—from contact forms to WooCommerce receipts—are just going to work better. Less spam, fewer delivery errors. For developers, it means we can rely more on the core function and spend less time debugging weird server-level mail issues. If you were using a filter to work around these problems, you might be able to simplify your code. For instance, if you were forcing a ‘from’ address, you might still need this:
add_filter( 'wp_mail_from', function( $from_email ) {
// Check if the from email is the default wordpress@...
if ( str_starts_with( $from_email, 'wordpress@' ) ) {
return 'your-real-email@yourdomain.com';
}
return $from_email;
} );Look, this stuff gets complicated fast. If you’re tired of debugging someone else’s mess and just want your site to work, drop my team a line. We’ve probably seen it before.
The key takeaway is this: core updates matter. Relying on plugins to patch fundamental platform issues is always a temporary fix. When the platform itself gets better, the entire ecosystem benefits. Trust me on this.
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