update to 5.3.1 broke emaliing

I had been testing 5.3 very successfully on my test web site on my local computer before taking it to the main site. (there’s nothing there yet to show or ask about specifically as I had to start again… ?? ).

Every worked and was great.

I installed to the main site today (knaphillbaptist.org.uk) and got 5.3.1. This doesn’t send emails – it fails with the message “There was an error trying to send your message. Please try again later.”

Repeated the exercise on the test site. Broke. Deleted it and uploaded a copy of the 5.3 code and everything is fixed… (it wasn’t enough just to overwrite the code with a lower version – it had to be deleted, suggesting it’s a setting in the database? )

Any help you can provide would be great!
Thanks

Eric