I am looking at emailarchiverpro and emailarchiverpdf. They appear to be the same company. Does anyone have an opinion on one or the other? Dave_Palmer, can you tell me how much storage these archives take on your computer?
I keep email as email… the reason is quite simple : email on macos are saved as mbox format which is basically folder and email as text format. this is the default format since mail has been invented. and I guess this is the format that will be still in use in several years. Recognizable on any email program or email server.
You could for example open an email address on a provider of your choice, set up this account on your email app, and duplicate email you want to this new account, think this account as an Archive. Doing so, you keep also the metadata (who sent, when, which server and date, and other technicalities which could add more “proof” is this email is important.
You can find and back up this folder at /home/Users//Library/Mail/V5//INBOX.mbox
is one email account. You may have more if you set up others 
Thanks! I’m experimenting with archiving in DevonThink.
And sometimes I think about trashing all of it
IT Takes about 20% more space as it stores the atttchemnts as PDF’s
Two other options are EagleFiler and MailSteward. Both accept Apple Mail or mail exported in the standard Mbox mail format. EagleFiler says its live search is faster than Spotlight, and you can search mail as well as attachments. I use EagleFiler as a general shoebox app, for everything from notes to pdfs, images, etc, and the mail archiving was just a bonus.
I used MailSteward a decade ago, when it had a much more Windows-database look to it. It’s an extremely powerful one-trick-pony, available in free/standard/pro versions ranging from $25-$100. It can easily handle multiple mail accounts and hundreds of thousands of messages (millions for the pro version) and you can even use it to schedule automatic ingestion and archiving of email messages.