Based on the way search works with the search index being updated in the background after mail is appended to a folder. It is unlikely that the indexing is complete when you first open the folder. So a search using Ctrl+K is unlikely to work well, if at all. In half an hour it might be a very different thing. (status of indexing can be seen if you look at the activity manager. It is on the Tools menu)

A quick filter search using Shift+Ctrl+K will search the immediate folder without much fuss, it will be slower and less configurable.

You could do a find search Ctrl+Shift+F this is essentially the search from Thunderbird V2 and is perhaps the most flexible. The limitation is the search occurs in the find dialog not in the main user interface. Searches can be saved as virtual folders, but that is probably not what you want as th archive will not form a permanent part of the profile (or I assume not from your question)

But those are your three search options in Thunderbird.

Thanks for the quick response! This makes sense. The advanced search using Ctrl+Shift+F looks very useful. True, the archive probably won't be part of a profile but we may sometimes need to save and be able to bring up those results quickly multiple times.

I made numerous assumptions, but really I do wonder why anyone would want to archive mail outside of a profile in these days of cheap disk storage. While folks might not want to use huge space for mail on expensive SSD drives, you can locate your profile on a cheap platter disk and stored gigabytes of mail all in the profile.

I would however recommend against anti virus scanning of large stores as it can grind things to a halt. I would also think you probably should have a fairly large amount of memory on your device 16gb+ on a 64 bit operating system so the indexes of the mail don't run out of physical memory. Keeping individual folders at manageable levels (less than 4Gb) is probably also a bonus for performance.

You can also use a separate profile just for the archive files, and run two instances of Thunderbird one with your current mail and one with the archive.

Thanks for the recommendations. The use case is probably an unusual one.

We are a mid-sized company using Google Suite for email/calendar/etc. When an employee leaves, we still want to retain the mail history. Google does have a Vault solution for this, but it costs an extra licensing fee. Keeping the mailbox of former employees online also consumes a license.

Google does provide a method for exporting the mailbox and downloading it. This can either be exported as PST files which have a max size of 2GB, or MBOX files, which can be up to 10GB. We can then upload this back to Google drive (unlimited storage). Doing this is time consuming grunt work (and in theory could probably be automated using available API's) but doesn't cost any additional license fees. I'm using MBOX format purely so that I don't have as many individual files to move around.

Most of the time, those MBox files just sit there on Google Drive. In theory, they will be deleted after 7 years. Rarely, someone needs to search those old mailboxes for a specific email. Since they are in Mbox format, Thunderbird seems to be the best free option.

This goes against a number of good practices. But I assume you will not be adding or removing mail from individual folders so that in itself will mitigate almost all of the risk. I would also not expect huge turnover in staff so perhaps one new mail archive folder par day at the most.

Synchronized storage is a mess really as Thunderbird does not have any concept of a file not being local and available. So it is not really recommended. But in this instance it might work. Simply because of the stability of the files involved. No rel changes, just some new folders added every now and again.

You say the files are on a Google drive. I am assuming in a structure like Archives\USERNAME\mail mbox files. For this I would suggest you sync them to a local folder. Again because of issues with remote access not being well understood, let alone tested a synchronized store is preferable I think although it will not be all that useful while new files sync.

Now create a new profile in Thunderbird. Add an account as it really does not function well without at least one "real" mail account to send from if nothing else. Make it imap as that will make this easier at the file level. The storage folders for IMAP and pop account are separate and "local folders" is for this purpose a pop account.

Go to the account settings for local folders. Under local folders you will see a local directory. Change this to the root of the mbox store. Say Archives\ from my assumption above.

If you allow the synchronization to occur when you add new files to your archive, they will automatically appear in Thunderbird local folders. Sometime however a restart is required to "prompt" a re-scan of the file system to update the folders displayed. Deleting the foldertree.json file from the profile folder will force the issue if it does not happen when it should.

I hope you understand that lot. It is a lot in a little bit. But I think it is as close to automation as you will get. Without messing around.

I should have been more clear. The files are stored in Google drive for long term storage (kind of the way tapes were used in the olden days of a few years ago). When someone needs to look at the files, they are downloaded from Google drive to a local folder. This happens very very rarely. I have over 400 archived user mailboxes, and have dealt with maybe 3 requests to review archives. The real reason for keeping the archives is for legal reasons (In 20 years of working in IT I've only ever had to supply records to satisfy a request for a lawsuit once, but really don't want to not have those files the one time it happens). The occasional request to search for an old invoice or whatever is a side effect. I really wish managers and users didn't know they could ask for it, but unfortunately not my decision.. Anyway, thanks, this is still useful information in figuring out the best way to provide access when necessary.