If any of your postal mail from Computershare bounces, you get a special "Mail Returned Unclaimed" status for that holding and you won't receive some future mail. (they just told me on the phone that "important" mail will still be sent, which I take with a grain of salt)

The problem is, they don't notify you at all if this happens. You only find out by either logging in and viewing that holding, or as I did, realizing you haven't received some mail that you should have.

So watch out. Periodically check the Holding Summary page for each of your holdings. Look for the line "Mail Returned Unclaimed: yes". It's not in bold or anything to make it stand out.