Steps to Repro:

1. Setup email archiving (Mail+Archiving+FAQ).
2. View a few emails.
3. Add a new page.
4. Using the RTE, add a left bracket, aka "[".
5. This should bring up the Link Suggestions tooltip menu.
6. The menu should show suggested links to the emails you recently viewed.
7. Click one of the suggested emails.

Expected:
The Link Suggestions tooltip menu goes away and a link to the archived email is added to the page.

Actual:
The Link Suggestions tooltip menu disappears, as does the left bracket you entered, and no link is added to the page.

I doesn't appear possible to link to archived emails within Confluence. However, the Link Suggestions dialog should not offer these pages as suggested links if they don't actually work.