Unusual Sending Activity Detected

Unusual Sending Activity Detected

My wife's account ( wanda@goevolve.com) was blocked when she tried to send the same email to multiple recipients.

She does this about once a quarter. What is the limit to the number of addressees on a single message?

How can she easily send a single notification email to a little over 100 people once a quarter? 

Please help.

Thank you.

Scott