Thunderbird stores mail exactly as it arrived, so attachments are stored as mime encoded text internally in the individual email. There are no attachments as such in existence even, so obviously no folder with them in.

hi matt. thanks for this. a follow up please? so the attachment (a 3D file type or a zip file or a pdf or whatever) is sent to me. then what? i “access” it using TB on the mac (or PC or whatever). and it sits there? what is mine encoded text exactly? and how do i access it “after the fact”? also, if i am RECOVERING or CONSOLIDATING old profiles using IMPORT EXPORT TOOLS - do i need to do anything special to make sure the attachments come into the new consolidate profile? sorry i know some of those are dumb but i am trying to reclaim my email here if i can..

Simple questions, but how to answer without a book. A bit like who won world war II and who came second really.

Email is strictly text based. Lots of tricks exist that allow mail of all kinds to get around, mime encoding being really the core of it. Binary data is re-encoded using MIME as Text for incorporation into the email body. See the wikipedia explanation of MIME. It is a good starting point. https://en.wikipedia.org/wiki/MIME

The next part is that email consist of only two "parts" email headers and the body. Everything else is an abstraction from that point, largely supported by MIME. Given that usually the only part of headers people see is the Subject:, From: and To: information, just about everything folks usually consider to be email is "the body" (or content although that is not the term used in the RFC's).

The body of an email consists of, as I said text, interspersed with binary mime encoded objects.

To use as an example the email I got from the forum announcing the content of your last post.

looking at the message source (ctrl+U) shown many headers including

Content-Type: multipart/alternative;

boundary="===============1565289715385939633=="
MIME-Version: 1.0

This tells the mail reader software that the message in MIME encoded, not simply plain text and where the boundary is.

Then in the body there are blocks that appear that delineate "parts"

Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

Identifies the following block is text, what character encoding to use and that the encoding is 8bit.

Later in the same email we see

Content-Type: text/html; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

Which identified the following block as HTML.

IANA ( Internet Assigned Numbers Authority) maintains a list of registered MIME types.

Really I would suggest you access the source of an email with an attachment.

You will find a block at some point with this sort of thing.

Content-Type: application/pgp-keys;
 name="0xF0B3DEEB56268743.asc"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
 filename="0xF0B3DEEB56268743.asc"

The only difference between an embedded image in say a signature and an attachment is how it is declared in the "Content Disposition"

So to answer the direct questions, the import export tools import "the mail" so no you need do nothing extra. Accessing the attachments requires you to open the mail, either in Thunderbird for mbox files, although very early versions of mac mail also used that same file format, among others. Of interest is at it's heart mac mail still uses the format, but wraps other information into a zip like structure that makes up the mac mail file. Mac mail still offers to ability to import MBOX files, you just need to put the file extension on them to make the software aware of what they are. What I am saying is you can direct import the files to mac mail.

Most mail programs including mac mail can open individual EML files. So mail exported from Thunderbird into EML format is probably the most "portable" as it is not really product or version dependent and is almost universally recognized as an email and opened by the default mail program. Be that on Windows, Linux or OSX.

To answer the anticipated question the difference between an MBOX and an EML file is that the MBOX stores many EML files one after the other in a single file with a designated "record separator" In the case of Thunderbird RD MBOX format that is a specially formatted from line. Wikipedia is helpful here https://en.wikipedia.org/wiki/Mbox Do you think I can dispense with your other topics and we can just work on the one. I get confused having multiple related questions with the same person at the same time.

Loading older profile in Thunderbird 68. is as simple as going to the help menu, selecting troubleshooting information. clicking the About:profiles entry at the bottom of the first block of information.

Once you have your profiles listed, select one, and instruct Thunderbird to open in a new browser. If it is not listed, create a new profile and point it to the old location. I talk about that in my blog here

Thunderbird's default is to add to the collected address book every new contact you send mail to. It does not do that for incoming mail. So unless you chose to not have that happen each new email address you send to is added to that address book.

I would be interested to know why you use mac mail now. What is it offering Thunderbird does not? Just my curiosity being busy here as the only thing I am aware of that it does better is write access to the mac address book, and that is a limitation imposed by apple I think. (I am not an apple person. I actually used an ipad recently for the first time, so be gentle.) Personally I have as much difficulty with the apple tax as I do with the Microsoft one. In both cases you pay about 30% more for the branding. So I try to keep familiar, but I will not be converting :)