So, I found I couldn’t send emails from my earlymodernweb accounts via my btinternet outgoing mail server. Next step: change the settings to use the earlymodernweb server instead. Irritating, but seems straightforward enough. Except that that gives me another set of error messages, “sorry, that domain isn’t in my list of allowed rcpthosts; no valid cert for gatewaying (#5.7.1). Please check the message recipients and try again”. What on earth does that mean?
For fuck’s sake.
(Final update: finally fixed, fingers crossed, with the help of Google. But why do error messages have to be so incomprehensible?)