Unable to send the same email to more than 6 people at the time

I have been trying to send an email to a big group of people, but unfortunately it always marks error and only let’s me send the email to 6 people at the time. Does anyone know why this might be happening?
Thank you

Are selecting or entering their email addresses individually? If you can, put the email addresses in your contacts and assign them all to the same label. Then send the email to the label. I know sending to a label works because I use it every month. I don’t know about more than six people though because that is all that I am sending to.