So, if I've understood, the phone being out of support from the manufacturer is the issue.
So far, I've got the Gmail app sending again but there's still a problem with synching (I think) which is resulting in the sent folder being empty and sent messages not being saved. That was done by changing to "accept all certificates", presumably including out of date ones.
My go-to email client is Outlook for Android and there I can't edit the account settings. It seems once set they can't be changed. I'll have to delete the account and try starting again.
