Setup mail reception limits

[renegama]

Many mail servers has a "send emails per hour" limitation, like no more than 500 mails per hour or less than 5 connections in 10 minutes, etc.

Would be nice if Papercut could have that setup so developers could test applications against those limits.

Recently a customer change from "internal email server" to a hosted one and several internal messaging applications are having issues delivering emails for those limitations.

Thanks