your could use pop mail instead of IMAP, or you could copy mail instead of move it.

Thank you for your answer, but I need to solve that problem if we want to go on using Thunderbird. It's pro, I cannot change the pop/imail configuration and we all need to be able to sort those same incoming emails on our computers.

You may be able to resolve the issue by adjusting:

Specify when messages are automatically marked as "read" Menu location: Thunderbird | Preferences | Advanced | Reading & Display

https://support.mozilla.org/en-US/kb/configuration-options-viewing-messages

There is an outdated article at: http://email.about.com/od/mozillathunderbirdtips/qt/et_mark_read.htm that may provide helpful background, although the menus have changed so the options probably have too.

Izy, I am not sure what you think your asking, but regardless of the email client two things are immutable. IMAP is a common protocol that works the same on all clients, it is synchronised If your using this protocol your only option is to copy messages not move them Simple really. ie what is in the inbox stays in the inbox for ever.

What I am saying is either modify the protocol or modify your work practices to accommodate your refusal to change mail settings. There is nothing anyone in this or any other forum can do to help you with your issue as you set requirements that make what you want unachievable.

@rdela: I didn't find a way to mark it unread permanently, I'll see if marking them unread for a long period is enough. Thank you for your help.

@Matt: I know exactly what I'm asking for, as it works on Outlook for example. You can have one email distributed on several computers, that I cannot do with Thunderbird very unfortunately. So what I ask is not unachievable, and as it is work I cannot just copy emails. Thank you for your answer.

Your know exactly what your asking for. Congratulations.

Use Outlook is the obviously solution. But be very sure Outlook can do it without the Exchange server. Most of it's tricks fall flat without it as Outlook can actually do very little without exchange, other than make a very poorly fitted internet mail client and lead the world to believe Internet E-Mail is something it is not...

@Matt’s initial reply may be your problem. Are you sure Outlook was set up to use IMAP and not POP?

IMAP is a newer protocol that keeps mailboxes in sync. POP does not and must be explicitly set to leave messages on the server for a period of time long enough to allow other clients (the “colleagues Inboxes” in your case) to fetch and store them.

For more explanation of the differences, see

IMAP - MozillaZine Knowledge Base

or

Use IMAP or POP E-Mail Programs (help.outlook.com)

or

Get started with IMAP and POP3 - Gmail Help

If that is the problem, see

Changing IMAP to POP | Thunderbird Help

to switch the accounts to POP from IMAP, just make sure you leave the messages on the server long enough for the other computers to grab them, but not so long they fill up your allotted mailbox storage

Using webmail with your email client - MozillaZine Knowledge Base

> If you check "Tools -> Account Settings -> Server Settings -> Leave messages on server" you can access your mail both from Thunderbird and from a browser. You may want to set the number of days it keeps a copy to avoid filling up your webmail mailbox.

IMAP accounts should have the same menu commands as POP accounts - Common misconceptions about Thunderbird - MozillaZine Knowledge Base

> POP and IMAP accounts are quite different. You read new mail in a POP account by downloading it from the inbox. It has a very download-centric view of the world. You read a new message in a IMAP account by opening a remote folder on the server. It only downloads message headers. It has a client-server view of the world. That's why you can do things such as read mail in all of your folders and upload messages.

> A POP account needs settings such as "keep messages on server" because, by default, it downloads them to the hard disk and may delete the original (it depends upon the "leave message on server" setting). There is no need for those settings with an IMAP account because it keeps the message on the mail server when it reads it. It fetches a copy which it stored in memory, but never stored on the hard disk.

> Tools -> Server Settings -> Synchronization & Storage -> "keep a copy of all messages for this account on this computer" is something completely different. It creates a optional offline folder in the profile which has a copy of the folders messages. You can't read those messages unless you're working offline and they had no effect on whats stored on the mail server.

see also

Specify whether messages in a folder should be downloaded for offline access (IMAP folders only) Menu location: Edit | Folder Properties | Synchronization

Manual Account Configuration | Thunderbird Help

And if all that fails there is active Community-powered support for Mozilla Messaging on Get Satisfaction in addition to this forum.