For all email external to the SBS server, email delivery is delayed by 30-60 minutes. In todays world, people expect e-mail to arrived within a minute or so.
Background information: I recently completed a SBS2003 to SBS2011. Since the migration, email delivery via the POP3 connector has been problematic. Email does get delivered into exchange mailboxes but it might take 30-60 minutes or so before it shows up.