looking for some help!

I have in past had no issues sending mass emails through salesforce. However, today I was trying to send an email to a few select individuals while filtering with roles and I received this message telling me that the email content size was too big. This is confusing to me as I sent the exact same email two days back and I was just following up with those who I forgot to send the mass email to. So there should be no reason why I am receiving this message telling me my email content is too big and that it will cut off part of the email if I was to send it via mass email. Luckily it was only 8 individuals so I just sent the email individually but that defeats the whole point of being set up on salesforce in the first place (to eliminate tasks as such).

Looking for insight as to why this might be and if I need to change any settings on my part to not receive this message in the future.

Word for word, this is the message that I received: 

"Just a heads up...

This email template contains too much text. Remove some text and try sending again. Or if you decide to send it anyway, some text will be cut off in the received email."

thanks in advance for your help!