Re: It slows down considerably once you get to multi GB mail storage
There's a trade-off though, speed vs corruption. The bigger the file store, the more it is susceptible to corruption. In my experience TB is a lot less susceptible to corruption than Outlook. Put another way, Outlook pays less heed to boundary conditions than TB. Microsoft appear to acknowledge this...
"Note that .pst files are not meant to be a long-term, continuous-use method of storing messages in an enterprise environment." (Microsoft).
The crazy thing about email is that it really should be stored in a proper SQL database for the best of all worlds, speed, integrity, security and accessibility even over LAN/WAN links. Archive utilities do of course exist but the ones I've seen are not intended to replace the email client.