Are you using a POP account?

If so, right-click the account name on the left, choose Settings > Server Settings, tick "Leave messages on server" and untick "Until I delete them".

Does that help?

Thanks for your comments. When I downloaded Thunderbird, it automatically set it up as an IMAP account. Then the setup screen does not have a box for "leave messages on server". Is there a way to override and set up as a POP account? It is set up as a POP on another PC using Outlook.

IMAP doe not have a setting to leave messages on server, since it does so by default. However, there is a setting for When I delete a message for accounts set up as IMAP, but the available options should not remove them from the server either.

You could of course set up the account as POP in Thunderbird by adding it as a new account (while leaving the IMAP account untouched first), but that’s not the normal method, and you may still want to allow one POP client to remove them, or neither of them instead.

Both POP and IMAP protocols can be used at several clients, but leaving messages by the POP client is important. Are you sure Outlook on the other PC isn’t the client removing them, so that Outlook needs to be set accordingly? Don’t forget any other clients capable of doing the same, such as a phone.

The only other option I could think of is a message filter in Thunderbird set up to move the message elsewhere. You could also look at the Activity Manager (in the Tools menu) to see if messages are actually deleted or moved after retrieval.

I believe that your first statement answers my question. We are able to open email on one iPad, two iPhones, one PC with Outlook, and this PC with Thunderbird. Just as you commented, Tbird is indeed leaving messages on the server. Only the PC with Outlook (POP) is removing messages. Thanks so much for your help. I have another question regarding how to transfer my Outlook address book to Thunderbird on this computer. But I should probably set that up as a new question. Thanks again.

Good to hear.

Well, when at it: for importing Outlook addresses (by exporting them from Outlook first), please have a look at the Switching to Thunderbird article. Does that help?

Please mark any of the messages above as a solution if you’re satisfied.

Thanks for this info. I looked at your reference article, and will try it soon.