IMAP uses port 143, but it seems 993 is recomended.

Port 993 means IMAP using SSL/TLS which is highly recommended over clear text. You'll also need to change 'Connection security' from 'None' to 'SSL/TLS' in your Account Settings.

Thanks, tried that but it does not seem to make any difference. The old config had STARTTS with Normal Password rather than None

Opps. well it does now seem to have sorted itself out. So perhaps this has solved it after all. Thanks.

Well after more testing still not working properly

John

O dear, no it still takes for ages. Seems that some times it goes straight away but mostly fails. Messages are always sent. They are just not copied back to the sent folder.

Try to start Windows in safe mode with networking enabled.

- Win7 http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode

Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/en-US/kb/safe-mode

Does the problem go away?

Thanks for the info. I started by running thunderbird in safe mode (Windows in Normal). I then sent a message which failed to send (not often seen this before). Not sure if any of my add-ons have anything to do with sending but this is the reverse of what I would have expected. I then restarted the PC and sent a message (I assume no longer in safe mode) which went and correctly copied to sent folder. I am getting the feeling that some of the delay is caused because the PC is doing other things. The send normally (apart from above) seems to work, its the copy back to the sent folder that fails. The MS mail system is, I assume, cloud based. I do wonder if the PC thinks that received mail is a low priority job and is doing other things. We are on a poor internet link with a very long copper line (5000 meters). The other mail system I have is POP which asks me to down load or batches every 10 minutes and copies to send folder locally. This never fails. ie the MS cloud is new to me (a few months and I think the problems date from this mail system). As the problem can be intermittent I will work on the Safe Mode with Windows . Thanks for this tip. But it may now take me some time to find out what is really going on. Re my incorrect configuration for the 993 vs 143 and STARTTLS vs SSL/TLS. I wonder if perhaps it would be useful for a check to be built into Thunderbird so that it cannot mismatch; or perhaps a routine that can be run to verify the correct settings?

Still getting the unable to connect to the server message appearing

The send normally (apart from above) seems to work, its the copy back to the sent folder that fails.

As opposed to the actual sending via SMTP, with an IMAP account, the copy to the Sent folder actually happens via IMAP. That means the message is transmitted to the server twice: For sending to the SMTP server, for copying to the Sent folder to the IMAP server. There are server implementations which can handle that more intelligent, so that the message really needs to be transmitted only once. Google Gmail is an example. I'm not sure how Microsoft handles this.

We are on a poor internet link with a very long copper line (5000 meters).

That certainly doesn't help. If you don't need your sent messages on the server, you can tell Thunderbird to save a copy of the message in the local Sent folder underneath your Local Folders account. Check your Account Settings. Having sent messages on the server is one of the reasons to use IMAP though.

I wonder if perhaps it would be useful for a check to be built into Thunderbird so that it cannot mismatch; or perhaps a routine that can be run to verify the correct settings?

This is exactly what Thunderbird does when running the new account wizard.

Thanks, I will work on this. As I already had an email account in 1 name and simply changed the server (not my choice) I then edited the account details (under instruction) rather than starting from scratch and of course missed the account wizard step and apparently got SSL/TLS wrong.