i guess you think you are going to be making a local backup. If you are using IMAP that is a dream. Not only is it unlikely you will get a usable local backup in a single command, IMAP be it's very nature of being syncronised to the mail server will not deliver an archive of any value at all. As soon as the email is removed from the server it will be automatically deleted from Thunderbird.

Over time Thunderbird will download a local copy by default of every email in every subscribed folder, but you can not use that local copy as it stands as any sort of archive. You need to go one step further and actually export the mail from the account in Thunderbird to get an immutable local copy.

I recommend the import export tools addon for this process as it can export MBOX files of whole accounts in a single session, but it is relatively slow. The copies will take time to verify and validate currency with the server. It is however, I think, to best way to archive mail from an IMAP account in Thunderbird.You can later import those same MBOX files to Thunderbird in the local folders, but somply copying then from the account to local folders is prone to failures that are not noticeable at the time and can lead to major disappointment later when you find a folder is missing significant numbers of email and they are not not on the server to try again.

You also have to be aware Yahoo have a hard daily limit on how much bandwidth can use. As you are using that particular yahoo server (the export not the regular IMAP one) you will probably encounter it a number of times so expect days to elapse before everything syncs up. I their own words "it can take several days or longer to download everything."

Hello Matt,

Your detailed reply is *extremely* helpful and informative - thank you!

I intend(ed) to copy all of the folders to a local set to avoid losing them when I remove them from Yahoo's servers - at least that is a trap I was aware to avoid.

I was not aware of Thunderbird add-on you describe, and I will use that tool tomorrow. Your caution about time it takes to complete is appreciated (Yahoo appears to be periodically ratcheting down their (previously unstated) email storage allotment for "free" users that only pay by making subscriber eyeballs available to yahoo commercial advertisers (yahoo now wants direct fee payment going forward, and I'm preparing to vacate as I don't intend to take that path.) The next step-down in storage will affect my use, but even at a very leisurely transfer rate, the add-on should ensure the data is captured before that change.

Anyway, thank you very much for taking time to explain facets of my problem to me in a clear, understandable and helpful way!

Matt - wow, what an improvement!

I installed import export tools addon and it's flying through the download of my yahoo account. Yes it may/will slow down or whatever, but the simplicity of right click on my yahoo account in thunderbird and choose "export account" was literally what I was hoping for in my original post.

Thanks so much again!