re: old email address Not certain whether your old email address is linked to your ISP or not nor whether you have changed ISP. So have included info for all possiblilities.

If that email address was issued to you by your ISP, but you have changed to a new ISP then it is likely that your old email address will no longer be available or will soon be unavailable because you are not paying for the service.

If this is the case then get all your emails off the old server before this expires. If you had a pop mail account then all of those emails would have been downloaded to your Thunderbird mail account. You could move all of those emails into Local Folders before removing the mail account.

If it was an IMAP mail account, check you still have access to that webmail account - you must check this first.. If you do, then synchronise all folders to get a copy in Thunderbird. Then go into 'Offline' mode and move them into Local Folders. If you synchronise to an empty server, you will lose all emails.

If the old email address is not associated with ISP eg: gmail then you do not need to worry.

If you still have the old original mail account and it is fully functional with ISP or independent like gmail and have created a new email address with a different server, you can add a new mail account in Thunderbird for the new email address and have both incoming to Thunderbird. Thunderbird can have many mail accounts/email addresses all shown in the same Folder Pane.

If you want your new email address to get forwarded to the original email address (which is still fully functioning) then do this 'forwarding' via the new email address webmail account. There is no point in downloading email just to forward to another server and then download again.

Or

if you want the old email address to get 'Forwarded' to new email then do this via old email address webmail account. But remember it must still be fully functioning and available. 

In my opinion, it is a good idea to have separate mail accounts because if one server goes down - even temporarilly, then you can still get and send emails through the other mail account.

To offer further advise, I would need to know more about the old email address. Is it offered by your current ISP or old ISP or indendent like gmail?

Thanks. I have numerous links associated with my old email address, utilities, banks, insurance, etc. but I have now set up another address via the same ISP for reasons too complex to get into here, so I was hoping to gradually wean the users off my old address but need to keep it just in case some slip through the net. I have both the addresses shown on Thunderbird at the moment but need to switch between them, I just thought it would be neater in the long run if I just had the new address with all my e-mail being forwarded from the old.

Toad Hall said: if you want the old email address to get 'Forwarded' to new email then do this via old email address webmail account. But remember it must still be fully functioning and available.

…which means setting it up on the server.

"I have both the addresses shown on Thunderbird at the moment but need to switch between them" - why do you need to "switch"?

re: I have both the addresses shown on Thunderbird at the moment but need to switch between them. I agree with Zenos - what do mean by 'switch' ?

Have you gone and created a special new Profile for the newer email address and you have to keep exisitng Thunderbird to swap to another Profile to see the other email address mail? This is totally unnecessary - you can have more than one mail account /email address in a Profile. Create a new mail account for the existing mail account /email address, so that both are in the same Profile.

OR Have you added the newer email address as an additional identity to the older email address, so that you only see one mail account in the Folder Pane and you keep going into Account Settings, editing the server details etc and clicking on 'Manage identities' to 'swap' the one set as default?

Ideally, you should not be doing this on a regular basis. The settings are usually setup and left alone until really necessary to alter them.

I would recommend you create another mail account for the newer email address, so both are seen in the Folder Pane and remove the newer email address from the identity, so that the original email address keeps it's own mail account.

OR Do you mean you have two mail accounts shown in the same Folder Pane, one on top of the other? If yes, then perhaps you might prefer to have the new one positioned at the top. 'Tools' > 'Account Settings' Select the second newer mail account Click on 'Account Actions' select 'Set as default' This will position the newer mail account at the top.