Help! Email account won't work in Mail, across 3 devices
Hello,
I'd be so grateful if anyone can help me, this seems a really tricky problem.
Situation: I have a longstanding work email account which I need to access using the Mail app on three devices: a Mac Pro, a Macbook Air and an iPhone. All run different versions of the Mail app.
Problem: This email account is not working on any of these versions of the Mail app.
But, it works just fine when accessed via a browser and I've verified the settings many times.
History: the email account worked just fine for years on the Macbook Air but didn't run (also for years) on the Mac Pro. It ran ok for years on an old iPhone but I had to replace the phone and when I went to enter the details into the replacement iPhone, it wouldn't work. All three devices with all three versions of the Mail app are successfully running another email account (mac.com).
Details: the Mac Pro is running El Capitan and Mail 9.3; the Macbook Air is running Mojave and Mail 12.4; the iPhone is on iOS 13.7.
The accounts were linked via iCloud and I suspected a problem may have crept in on one device and become copied across all, so once I knew I could access this work account via a browser, I deleted the accounts from iCloud and re-entered the account details. This did not work and the account now doesn't work on any of the devices.
Mail variously reports that it can't log in to the server, or the password and/or username are incorrect (they aren't) or, more interestingly, that Mail is unable to send the password securely. In the latter case, after a long think it offers the option to continue by sending the password unsecurely. When I choose that option, I've had the incoming mail work (but very slowly) and then stop working. I've not managed to get it to find the outgoing mail server. Right now even the incoming isn't working.
I've verified the account settings with the provider. They are as follows (anonymised, obviously):
Secure SSL: yes
Username: name@othername.co.uk
Incoming server: mail.nameothername.co.uk IMAP port 993
Outgoing server: mail.nameothername.co.uk SMTP port 465
IMAP and SMTP require authentication
My IT support is able to set up this account no problem at all on her machine running Mail and also to access it via a browser, so it looks like the problem really isn't with the settings but is somewhere at my end on one or all three of my devices - weird, huh?
I've done everything I can think of with the advanced settings (relating to SSL, and the tickboxes about automatically detecting settings, etc) to no effect. I also tried removing the com.apple.mail.plist file (and others that looked similar) on one machine, to no effect.
The email account provider is not being helpful - they just tell me to upgrade the OS to Catalina, which is not an option on those machines, which are at their most recent possible updates. I'm certain it's not related to updates: it was running fine until yesterday on the MacBook Air and the problem exists on the brand new iPhone (iOS 13.7).
I'm out of ideas. Can anyone help?
Thank you!