What's wrong with cloudflare?
Nothing really, but I'm wary of overcomplicating things. That said, can't argue with results. CPU usage plummeted when I switched over.

I was still seeing 503s though. Digging in deeper, there was indeed a problem with zombie processes eating up server resources. It looks like SMF does a hostname lookup for every connection, for ban and logging purposes. They time out, but slowly. I disabled that feature and our numbers returned to normal.
It looks like SMTP mail is broken. I thought it might be from the certificate changeover (mail.cutey.zone is now covered by the CF Origin cert instead, which won't work), but actually, I think SMF just crafts really spammy-looking messages. I ran a separate PHPMailer test with mail-tester.com and we scored 10/10. Sending a password reset request through SMF triggers a SpamAssassin scores around 20 every time though, which is bloody high.
Not really sure how to fix that. I could try updating SMF, but the addons we use literally makes changes to the forum source files and it's the most cursed thing I've ever seen. I'm sure an upgrade is doable, but it'd probably break all the themes and addons and make people sad.
On the plus side, while reviewing things I discovered that I named the sending email address Parakarry, which I find delightful.
