As TCH-Thomas stated, there is a mailing limit at TCH that is (in my opinion) pretty strict. When you exceed that limit, all outgoing mail for your domain is halted. That may be a problem, not just with lists but also with with regular email. For example, you can reach the TCH limit if a single user attempts to send an email to a large list of recipients. Suddenly, and without any notice, the emails sent by other users on your domain simply stop and may never reach their destination. I restrict the number of email users at our domain to help avoid the email limit problem.
For our lists, we set up Dada Mail. Dada Mail will trickle a few emails out every minute.
Hope this helps. -- Justin