Trying to explain the goal. You have a large email correspondence that is research, not public because it is raw form, discussion, etc.
The two (or more) people are always searching their email folders for the best methods of study and checking. However, that does not allow a simple URL to access email-by-email. (Maybe there is some Mailbox program that does something here, making each email to a file, I am using Eudora with the .mbx format.) You are always referring to subject and date, or cutting-and-pasting. A bit clunky.
You can put the emails into a Yahoogroups or Google groups. The big difficulty (beyond some privacy concerns, wanting this to be unseen by non-members, but at least Yahoogroups, probably Google also, seems to be pretty good on private groups) is that inline pictures are handled very awkwardly, if at all. They go through to the receipients, but not to the forum post online (in google they are morphed to .jpg attachments, YG simply strips them, dunno about any other forum alternatives).
Possibly there is a private blog idea that would work (cut-and-past) or you set up your own website with a CMS (content management system). The quick and easy CMS is possibly the solution, but it has to allow a quick and easy cut-and-paste, including the pics .. then you can Linkman keyword the urls.
Similarly, possibly a private VBulletin (or one of the other forums) section would do the job. Would this be as good as a CMS ? Dunno. I have a VBulletin forum, but have not tried this yet, one problem is that you are not really trying to create a forum thread, so each email would become its own thread. You normally do not think of web forums in that manner, that might only be a rethinking issue.
Anybody using something that they think would do this no muss, no fuss. Assume a quantity of about 1000 emails to be archived ! As I wrote this up, I realized I should try the VBulletin method, and see if the inline pics take and if it works good.