Hey there,
"It all worked fine for years." A reader emailed me that line last week, about their WPForms notifications, which had started bouncing back with a 550 error for no reason they could see. Nothing on their end had changed.
A 550 isn't your site failing to send. The email goes out fine, gets all the way to the recipient's mail server, and is refused at the door, permanently, so it won't sort itself out if you wait a day and try again.
The "for years" part is the useful clue. When something works for years and then suddenly stops while you haven't touched anything, the change usually happened on the receiving end. Which is more or less the story of email lately: Gmail, Yahoo and Microsoft spent ages warning everyone they'd start requiring proper authentication, then actually did. The setups that had been getting by without it are the ones that began to bounce.
It's worth reading the full code before you change anything, because a bare 550 can just mean the address doesn't exist. But a 550 5.7.1 or 5.7.26 means the message was rejected on policy, which nearly always comes back to authentication. You'll find it in your WP Mail SMTP email log, inside the bounce message.
With WPForms notifications, I'd look at the From address first. It's easy to end up sending those from an address that isn't on a domain you've authenticated, like the visitor's own email from the form, or an admin Gmail address. To a receiving server that looks like spoofing, so it gets turned away.
The fix is to send from your own domain. In WP Mail SMTP, set the From Email to an address on an authenticated domain and switch on Force From Email so nothing overrides it.
If that checks out and they're still bouncing, look at whether your domain has landed on a blacklist or your SMTP credentials expired. But for forms, the From address is the usual cause, so start there.
I wrote up the full diagnostic, including a decoder for the 550 codes, over here:
Read the full troubleshooting guide →
Talk soon,
Rachel
Product Educator, WP Mail SMTP
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