How many emails can I send at a time?
Under the standard setup, Google imposes a limit of 2,000 sent emails/day for trusted G Suite users, and 500 emails/day for regular Gmail users. There are other factors that determine sending limits too, such as the age and reputation of your Gmail account.
GMass allows you to send unlimited emails by sending through an external server like Sendgrid, and GMass allows you to artificially break Gmail's limits when sending through Gmail by distributing your emails over multiple days if your campaign exceeds your account's daily limits.