Risks of mass sending
Front does not have a sending limit, but depending on the type of channel you are sending from, you could run into issues when trying to send a high volume of emails at the same time. For example, there is a rate limit for API-based channels, recipient limit for Gmail channels, etc.
You can find more information about Google's sending limits here.
When this happens, Google returns a generic error making it hard for Front to tell you exactly what's happening. So, if you experience issues while mass sending, please look in to your email provider's sending limits.