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. Customers who thought their orders had vanished were filing angry support tickets, and that is the kind of thing that kills trust in a business fast. My first thought was, “Okay, classic WordPress email reliability problem.”
My first move? Set them up with a proper SMTP service. That is the standard play, and it usually cleans things up. But even after routing everything through a transactional email provider, a small but real number of emails were still getting flagged by aggressive spam filters. The root of the problem was not just the server. It was deeper, 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 is a core part of WordPress, but it has had some long-standing issues that often need workarounds. As detailed in the official WordPress Core dev notes, WordPress 6.9 finally addresses some of these headaches directly, no more band-aids. For the full breakdown you can read the source at make.wordpress.org, but here is 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, WordPress had a bug in how it handled multipart messages, the emails that carry both an HTML and a plain-text version. In certain edge cases it 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. 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 simply going to work better. Less spam, fewer delivery errors. For developers, it means we can lean on the core function more and spend less time debugging odd 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 takeaway: core updates matter. Leaning on plugins to patch fundamental platform problems is always a temporary fix. When the platform itself gets better, everything built on top of it benefits. Trust me on this.
