I would appreciate some feedback comments on the following.

If you use DMI which places all the emails you require into Daylite then Daylite can become your email archive.

Therefore based on whatever you think is convenient you can set a rule to delete all emails in Apple Mail that are, say, older than 3 months because you can retrieve them in Daylite. In fact you could argue that its better to include email attachments in the Daylite file because you can use Daylite as your archive & avoid duplication elswhere??

Interested on how others deal with this.

The only problem I see with this is a horrendous amount of emails that really don't say much, but are 'archived' anyway, and simply taking up space.
I don't have DMI automatically link every email. I pick and choose which one's I want to save permanently in DL. I delete everything else within Mail, but don't empty the trash automatically. It stays in my trash for usually about 6 months, sometimes more, just in case I need to retrieve it. After that, it's simply deleted/emptied right in Mail.
This way DL isn't filled with quick one line answers to questions, confirmations, and 'stuff' that I really don't need, especially after 6 months or so.
Emails can consume a lot of space in DL.

I'm with Mike on this - I pick and choose what gets into Daylite via DMI. Only those emails with information that is clearly important to have with the contact, project, or whatever.

As for archiving in general, I use MailSteward to archive everything once every few months, and then clear out much of the clutter from Mail.