Can we restrict the users from sending the mail to a mail group which they are member of and they should only be able to receive the mail which was sent on that group.
Yes. This is possible via mail policies SkyConnect supports extensive mail flow control via policies which can be applied at a granular level of a user or a group of users (COS-Class of Service).
For more information refer the topic Mail Policies
Sometimes we need to send mails to the 200-300 recipients in one shot. In our system, how can that sender id be prevented from being blacklisted for spam.
Mithi SkyConnect is SPAM intolerant. Every mail incoming and outgoing is scanned by our clean mail service (SecureMailflow) and only clean mail are allowed in or out. Due to this the system never allows to relay spam and hence always maintains a very high reputation for its IP addresses.We have very large customers hosted on this setup who routinely send mail shots to their mailing lists. To put it simply, a user can send his quota of allowed mail in a day, and as long as the mail are clean, there is less likelihood of that ID being blacklisted by the receiving systems as a spammer. For outbound mail, we configure best practice DNS records like SPF to ensure that the reputation of the domain is high.
Is there a threshold to sending mass-mails per user or are there some users who can be given rights to send unlimited mails?
There is an email ID based rate control, which auto blacklists an email ID if it attempts to send more than the threshold mail a day. The blacklists are reset at 12 midnight. Some users can be exempted to send more mail than the threshold, but that too is a limit. There is no way to allow unlimited mail a day for any user.