Interesting. Your using IMAP which is a synchronized mail protocol and battling against the very design of the protocol to force a connection when you click for it. I doubt your ever going to get that to work. Thunderbird initiates a connection to delete the message from the server and in IMAP terms that is syncing.

Sounds like you want to use POP not IMAP.

Yes I suspect its synchronising when deleting. Think it does it when I move/archive email too. Very annoying considering we unchecked all options to automatically get mail.

I have had to create an email rule on the IMAP server to move all my incoming email into a Hold folder which is not visible in my email client, then write a script to move email from this folder to my inbox, and run this script via cron at 9am, 12pm and 4pm. So that way I can get new email when I choose, and not when the email client automatically does it.

I tested it in Postbox and Apple Mail, all of them do it so I suspect its an IMAP feature, although I would think an email client could be programmed to specifically not do this.

There is no suspect. It is a feature of IMAP.

Why are you using something totally inappropriate and then going to great lengths to make it do what it is not designed to do. Why not just use POP?

Have you tried just going offline in Thunderbird? (click the two monitors in the bottom left of the screen)

I hate POP! I dont know why. I think its because over the years so many of customers phone up for email issues when its because they use POP (multiple devices!). I have multiple devices and use webmail, and I am not sure if POP is the best solution even if I do "leave a copy of the message on the server". I also read it may be phasing out, but I cant comment on that.

But I am not sure what you mean using something totally inappropriate. What is inappropriate?

And I am not sure I can agree with "make it do what it is not designed to do". I know email is designed to download my mail, but I would argue it really should only download mail when I change its settings to say download mail "manually" or only when I click the Get Mail button. I mean, if I set it to not automatically download, then I would expect it to not automatically download email, but it is. When I hit delete, it automatically downloads new email.

It all comes down to email addiction... I have to keep my email client open as all my daily tasks have emails associated with them. So I work through emails downloaded that morning, then archive or delete when I finish it, and new email comes in and habit means I read it and get distracted and start replying, then new email comes in when I send it, etc.

I never thought of disconnecting it and going offline! I may try it. Although I cant sent emails at that moment. But do you know what, this script I wrote is working pretty good now. Its harder to get new email as I could just go back online if I didnt have it, and back to square one!