More of a FYI, but I think something is wrong with outgoing mail from using PHP’s mail() function.
I was testing a part of my site which utilizes the mail() function and I was noticing that my messages weren’t going through. So assuming it was just delayed, I waited an hour or so and then tried again, still no dice.
Logged in through SSH and check the mail queue (mailq) and noticed all the connections were timing out. Below is an example error that you see running mailq and they seem to be building up.