Question
How many total recipients can I specify in the To/CC/BCC fields in an email sent through Office 365?
Overview
At times you may wish to send a single email to a large number of recipients at once. In order to safeguard the system from abuse, Microsoft has implemented limits on the number of recipients you can specify on each email you send.
Answer
When using Office 365 as the sending mail service, you may specify a maximum of 500 recipients per email.
However, Mass Electronic Messaging Guidelines on campus limit mass email messaging to 250 messages a day.
If you need to send an email to over 250 users you may need to look into an email list. To find the appropriate list for you, please see the article KB0009131: Which type of account is best for your email needs?
Find out more about the limits of email service in Office 365 at this web page: