Brogan,
1. Using Default Setting for email as follows: DEFAULT + Set return path with -f parameter
(my Admin panel doesn't identify this as PHP, but SMTP is definitely NOT selected). This has been unchanged since our launch at end of 2015.
2. If ACP is Admin Control Panel (forgive my ignorance), yes I am seeing dozens of errors listed as: "Lost Connection to MySQL server at 'reading initial communication packet', system error 4 [alto system error 0]
3. One Yahoo email address, one ATT.mail address, one Gmail email address, a half dozen others all small domains. Not Hotmail, No Windows, no Outlook.