Connection failed to IMAP account

I’m trying to set up two IMAP mailboxes on eM Client. One is a Googlemail account - no problem. The other is with 123-reg.co.uk. The account sets up OK, and tests fine. But it won’t download any mail. Can’t see anything. The log says :

19:57:01 david@theComputerConsultancy.co.uk [IMAP] MailExceptions.ConnectionException:
19:57:01 (Connection terminated)
19:57:01 at MailClient.Imap.Synchronizer.ImapCommand.ThrowIfConnectionBroken(BasicResponse response)
19:57:01 at MailClient.Imap.Synchronizer.SynchronizeMessagesCommand.Execute(WorkerStatus status)
19:57:01 at MailClient.Commands.Command.Process(WorkerStatus status)

I can access the email account by webmail OK.

Help !

Hello,
could you send us logs please? Go to: menu Tools->Settings->Logging and check “IMAP” and “Network communication”. Then restart eM Client,
try to simulate the issue and send us (with reference to this topic) the logs using the same logging settings window. Thank you

Thanks for getting back to me. I have now fixed the issue - the 123-reg email provider uses legacy ports. I changed the ports, and all was OK.
What confused me was that the inbuilt “test” function shoed that all was OK when I was setting up the account in the first place.