sendmail error 452 Too many recipients received this hour

Question

We are sending hell lot of e-mails to our BREW devices ( in sprint network ) and after a while our mail server queues the messages and gets stuck. When we try to flush them,

Answer 1

This is called grey-listing. When you send too many e-mails (or more often - a certain number of e-mails where a recipient does not exist) a destination mail server does not black list you, but instead they temporarily block access from your mail server (essentially the IP address of your mail server). Usually this block is set for 1 hour but obviously can vary depending on the configuration.

You can do several things:

1. Contact the admins of the domain in question (e.g. postmaster@messaging.sprintpcs.com) and request your IP address to be whitelisted. (They may refuse)
2. Check/increase time e-mails can stay in your local queues (to have more chances of them to retry and finally get delivered
3. Add more public IP addresses to your server

Answer 2

That's from their server. It looks like email flood prevention.

One alternative is to use app-directed SMS's to get data to your BREW application.

Answer 3

It looks like the mx.messaging.sprintpcs.com is throttling you. Perhaps try sending your mail with different IP addresses to beat this. It is probably an attempt at spam control.