Our church membership software (Shelby Systems) has a group email function where you can send out mass emails via the SMTP server in Exchange. I had to allow relaying from my private IP address range in order for it to work, but there's a problem; it takes too long to send. I have a group of just over 300 people that I've been using as a test group, but it takes over an hour to send a simple plain text email to all of them. Shelby tech support says it shouldn't take but a few minutes to run. The membership records are maintained in a SQL Server database.
Can you think of any settings in Exchange 2003 that I might need to tweak to make the relaying go faster?