I belong to a number of newsgroups where I save technical data from that is in the form of email. 1. How can I save messages, with header intact, to a text file as I could with Eudora?

File > save as >File. It will be saved with an EML file extension but the content is plain text (if unicode can be considered plain text. Some ASCII purists say it is not)

2. When I start Thunderbird, what email is loaded into memory?

I am afraid I do not understand that statement at all. You can access the accounts you have added to Thunderbird in account settings. All accounts are available at all times. What is physically loaded in memory has to do with what is selected and what tabs are open. But the question as written is not something that can be answered generically.

I have 5 email accounts. When I check my email email is downloaded from all 5 accounts into there respective in box. I place a lot of email into separate folders. I probably have 200 folders. When I start thunderbird, does it load all 5 inboxes into memory, I think that it does. Does it also load all of the folders into memory? I am beginning to think that it does as my computer slows down. I have probably exceeded the number of emails that the program was expected to handle that I have saved. My computer has the maximum amount of RAM which is 8 M.

I have tried the select save as file for email. This produces a file that has a lot of "fluff" that looks like HTML. I would like to save a true text file as I could with Eudora so that I can save the text file, outside the Thunderbird environment, into a folder on my hard drive. An example is for equipment. I have downloaded a lot of manuals and other equipment information. I would like to add the relevant text file representation from my email to this folder. With the save as file option, I have to edit out at lease 75% of the file which appears to be HTML formatting. Is it possible to export the Thunderbird folder to text?

You confused me with your use of the term 'newsgroups' as that is a specific term for usenet organizations. On your question, have you tried the 'save as' and select 'txt' format?

That fixed the save as text. I did not see the file format dropdown.

Still have a question as to what email is loaded into memory when Thunderbird is started.

Indexes (essentially .msf files) for active folders are loaded in memory. This is just a fraction of the actual folder size.