Let us understand what is throttling first, Some ISPs limit their number of incoming emails for a particular period of time from a particular sender. In any case if they exceed the amount or time then their email campaigns are blocked resulting in bounce backs. This is generally called as email throttling. It is also called as "deferral". However this situation is temporary but again it depends, in such cases you will receive a message stating that the "user is getting too many emails at a gre...

No, generally there are no restrictions but if you are a reseller or a very high volume sender then we apply some limitations in order to avoid spamming activity.