Google Apps mailserver - works fine for < 50 messages; problems when sending more

Question

My asp.net (mvc2) web app webinar registration system sends emails with connection info. Currently we just loop thru the list of attendees and hit a System.Net.Mail.SendMail for each. We send mail via our GoogleApps account (non-premium).

My use case is to send < 50 emails at a time and the system's been working fine. On the occasions where the number pushes a 100 addresses I find error returns with the message:

Service not available, closing transmission channel. The server response was: 4.7.0 Try again later, closing connection. (MAIL) g31sm4823143ibh.4

Is this message specific to Google's servers (searched on the phrase - seems like 'no'). Is there a recognized 'best practice' for sending emails by code?

Answer 1

Could it be that gmail just notices that you're sending a lot of messages in a rapid rate indicating it to them you're a spammer (in their eyes)?

If you have hosting I suggest you talk with your provider and see what they can offer you or provide an email address with which you can send more messages, in a controlled way of course.

Answer 2

GMail definately has a sending limit.

I dont think its widely publicised, but it certainly sounds like you're hitting it.