Err, second query on new features

Watchlist
1) Can I setup the service to use my own script for sending email instead of the builtin one?
  b) Failing that, how does one setup the email server settings, including login details?  I'd prefer to set this up at the xwiki.cfg level if possible, as this will then map across to all virtual servers.

2) Will this send multiple emails (one per watch), or a single combined email per day?