TL/DR; POP3 false positives can really mess you up. Sort them out the minute you get ‘can’t log in’ messages
So I got my core domain/sub-domain up and running on the new host after battling with a) corrupt user.ini file and b) .htaccess with incorrect permissions. It took just short of 24 hours of downtime to identify and fix the issues and I really didn’t like that much downtime. Actually it took 23-1/2 hours of downtime to identify and 10 minutes to fix, then 10 minutes to test.
I went to bed a happy bunny. When I woke up this morning I ran checks which all came back green. Then I tried to log in to the core domain front end except I couldn’t even see the front end because I got a 500 error. So I tried the sub-domain and couldn’t see that either. Then I tried this website and couldn’t see that. All three properties returned 500 error messages.
So I got onto the host chat and asked the to look. They said they were all up and in the green then they went off to check something. Five minutes later they came back to say my Internet node’s IP address had been banned. They’d removed the ban and everything should be sorted. I checked. It was indeed all sorted.
I asked how my IP address could have been banned. They pasted a report that said it was due to repeated but failed POP3 login attempts. I checked my phone and yes, in my email client there nestled half a dozen failed login attempts on one of the new email accounts I’d set up against the core domain. Apparently the hosting infrastructure registered my IP as unfriendly and banned me from all domains in my hosting hosting account. Ooops.
Anyway, I’ve reset the POP3 password and everything’s great now. How embarrassing though.