What are your email policy and limits?
Unsolicited emails/SPAM are not allowed under any circumstances. You are allowed to send legitimate emails within certain limits, as explained below:
There is a 25 to 100 hourly email limit per domain sepending upon the shared hosting plan. If you send over this amount in any hour, emails will be dropped.
All our shared hosting servers have a 60 pop checks per hour limit per domain. If you go over this you’re likely to get a wrong password error message saying login incorrect. Just wait an hour and it will automatically unlock you. To prevent this from happening again, make sure to disable auto checking, or at least set it to something higher such as 30 minutes.
For complete policy, please view, http://www.mumbaihosting.com/hostingterms.htm