Google Apps has been working great for my SMTP needs via DNN for a while. Now that I have a fairly large userbase along with a forum, there are many email notices being sent daily.

Google Apps has a limit on 500 emails per 24 hours per smtp user, which sometimes cause a conflict with my needs.

In an attempt to fix this, I created 4 google app users to rotate the load and set up an SQL job every 8 hours to change the HostSettings data for SMTPUsername.

While the jobs are running and updating the data, the actual entry in DNN does not change. In other words, I look at the host settings tabel wnd it shows "mailer-02" but in the DNN Host Settings page, it still says "mailer-01".

Is there a way to force DNN to reload this bit of information via SQL?

Also I'm concerned about sending monthly newsletters now because I have about 40K users and obviously this is a nightmare to do with Google Apps. Are there any recommendations for a third party email service that integrates with DNN?

Who is hosting your DNN application?  They should be able to provide you with an SMTP server that is unlimited (or limited by total bandwidth). Otherwise any SMTP server should work with DNN, it doesn't really care.

Do you have your dotnetnuke setup so when a user registers to your site it sends them an email message? I can't find where to put my admin SMTP settings.