MemberGate strongly recommends that you do not exclusively rely on the "send email" function in your control panel to send out broadcast emails.
It is possible that your site gets reported for spamming.
Someone, on occasion may accidentally press the "Report as Spam" button as opposed to the "Delete" button when trying to delete your email.
Also, some people use the "Report as Spam" button to get off a list instead of unsubscribing.
If you are reported for spamming almost all, if not all of the emails from your site will be sent directly to their spam folder. This means that none of the emails that you send to that member will be sent to the inbox, including order confirmations, support requests, etc.
To prevent spamming (and also to not bog down the email servers with big resource demands) many hosting companies do not allow more than a few thousand emails to go out from your site per hour.
It may be hard to manage which emails were sent to which members during which hour. Plus, if you are reported for spam, your hosting site can choose whether or not to shut your site down.
ISPs also monitor emails for spamming. They look for multiple emails coming from an unrecognized IP in a short period of time. There is the potential that your emails may get blocked on suspicion of being spam.