Well, I just found out that Siteground who I just opened an account with one month ago limits mailouts to 400 pieces of mail per hour. They also queue mail on their servers, which i'm sure is fairly normal. However, I has just sent a test msg to myself through Acajoom, and it took 32 minutes to reach me. Not very impressive!
Can anyone recommend the best hosting provider for Joomla resellers, also with the ability to do large mailing lists (10k+) in mind?