As the OP has yet to even respong to any of the further suggestions, it's difficult to answer.

However the OP only stated they wanted to read and/or search the emails offline. No indication of replying/forwarding. Heck, I do that now with my offline mail retrieved via getmail using grep and emacs.

As the OP has yet to follow up other than ask "how," your question can not be answered. They don't state what client they are using otherwise. So to suggest to them as others have to use Thunderbird... what if that OP doesn't like TB? At this point the suggestion is just as useless as suggesting getmail. However, there is a lot more flexibility in the getmail solution than the Thunderbird.

I guess we have to wait for the OP to find out.

I'm going to set up getmail to retrieve some email & see how Thunderbird copes with it.

Actually, I suspect my previous problems might have been due to using fetchmail.
The names are rather similar.

You don't have to set up an account to open up a mailbox. With that reputation and so many posts I thought you knew that already.

Of course, but the OP is struggling with the concept of copying mails between accounts in Thunderbird (which he said he installed in the OP).

Assuming he manages to make getmail do it's thing ( ) how is the resulting mbox archive in an arbitrary dir going to help him?

I'm guessing grep and emacs aren't first on his list of mail reading tools, and the archive won't appear in a client automagically.

Well, anyway, even without getmail, I think his question has already been answered more than once. I don't see what's wrong with using POP and then placing the mails wherever he wants to.

OK - If I have an arbitrary mailbox on my PC (filled using getmail), how do I access it?

I created a test mailbox on my ISP's mail server and sent it a few random emails.
I then used getmail in simple POP3 mode to put the test emails in a maildir I had created on my PC.
This gave me a number of text files with very long names.
Each one contained some email headers + some occasionally readable text.

How do I access this maildir to view or send any emails?
Any attempts to use Thunderbird don't work.

And nor did I suggest he do so, use grep and emacs, that is. Just stated something I do, and without knowing the OPs intentions, guesses could be thrown widely.

JeremyBowden, a lot of files with long names? Are you sure you didn't choose a maildir format? If it's an mbox file, copying that file to Thunderbird's Local Folders directory is enough for it to work for me.

I chose a maildir format because it seems superior to a mbox format for a potentially large mailbox.
Is this going to cause a problem?

Thunderbird does not support maildir natively, and I don't know whatever happened to the extension that was supposed to do so.

I'll probably try Evolution then.
I thought single file mailboxes were "deprecated".

The GUI in Evolution isn't all that pretty, but it allows me to archive emails (in a variety of formats, including maildir).
More to the point, it allows me to forward (etc) archived emails in the same way as any other emails.

I'm not sure if this would suit the OP - but it allows me to archive my email.