This depends rather on what format you want to use to store the messages.

The safest route IMHO is to use the Thunderbird native .eml file format, which as far as possible stores your messages verbatim, including attachments. The downside is that you need an email client, such as Thunderbird, so be able to see the .eml files. Whilst eml is supposedly an industry standard, MS's email clients don't handle it well, so your store would not be useful to a huge proportion of the world's computer users.

Other options are to export your messages to plain text (which loses all the graphical content) or HTML format (which isn't always entirely accurate), or just to copy the mail store files, which are a variant of a standard known as mbox files.

The other consideration is your reason for placing messages on the CD. Is it to be able to refer to them, whiilst perhaps releasing space on your HDD, or is it a back-up against hardware failure? Each of these has an influence of the choice of methodology. Alternatively, if you want to move these messages to another computer, copying the whole profile might be a productive route.

Thunderbird profile article

For most of these export options, I'd be looking at the ImportExportTools add-on, which if you choose plain text or HTML, can also build index files which you can view in a browser. Recent versions also allow attachments to be preserved.

http://chrisramsden.vfast.co.uk/3_How_to_install_Add-ons_in_Thunderbird.html

Beware! A Thunderbird profile can often be several gigabytes in size, and won't necessarily fit on a standard data DVD.

Let me give all the information so that my question may be clearer. I recently switched from comcast.net to gmail.com. My Comcast account is still active. I have multiple email accounts on both Comcast and Gmail. In each Comcast account I have multiple email folders, for both emails that I sent and emails that I received. Some of the Comcast emails I wish to put onto a CD/DVD for archiving. Other email folders I would like to transfer over to a similar folder in Gmail.

I did a Google search on how I could do this, and was able to follow it to a point. I realize that I needed an email client, so I downloaded Thunderbird. On one account, I emptied my inbox and transferred all emails in one folder back to my inbox.

In Thunderbird, I created an account corresponding to the Comcast account, and was able to put all 609 emails into Thunderbird. Now I want to put all there on to a DVD (or several, if one DVD can't handle it).

Second case: I can create another account in Thunderbird and transfer another Comcast account to that Thunderbird account. However, with these emails, I would like to merge them with an existing Gmail account.

Are both scenarios possible? If so, how can I do it/them?

In advance, thanks for any help.

I'd be doing lots of drag-and-drop in Thunderbird to move valuable messages into the new account. (Actually, I prefer select then right-click|Move To rather than drag-and-drop.) In either case, you could Copy rather than move; if the comcast account is going to be closed, it probably doesn't matter too much if you don't empty it.

For the business of saving message for posterity, I really can't improve much on my previous answer.

Export your messages in whatever way seems appropriate to a folder on your HDD, or a USB thumbdrive, and then burn that to CD/DVD. I wouldn't try to export directly from Thunderbird to optical storage.

Sorry that I am so dense. I can archive the emails, but where are they after they are archived? Can I use export and how do I find it? I cannot find anything related to Thunderbird named "profiles." "Move To" doesn't give me choices except where I originally got it from (Comcast) or Trash.

I think I need more detailed help.

To export I'd refer you to my first answer.