Question

How many total recipients can I specify in the To/CC/BCC fields in an email sent through Office 365 and Google Workspace?

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. Microsoft is the main routing for email in addition to guidelines that will be enforced by Google when using their email service. 

UC Davis Campus Policy Guidelines
Email lists options
Bulk Mail Requests
Microsoft/Office 365 Email Blocks
Google Workspace Suspensions

Answer

• 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.
  Users can subscribe to a Sympa list or the campus bulk mail tool is an option. If a third party tool is used, please work with the UC Davis Compliance office for options how to that use the Mass Electronic Messaging Guidelines with it and your departmental IT for their approved software.
  • For additional ways to send out mail with less recipients, please see the article KB0009131: Which type of account is best for your email needs?
    
    
• For one time messaging, you may want to use the Campus bulk mail system. Bulk/Mass Electronic Mailing Process
  
  • Use of the system is governed by the UC Davis Mass Electronic Messaging Policy (Section 310-18) and the UC Davis Allowable Use Policy (Section 310-23).
  • Messages sent with this must have approval from the appropriate Associate Vice Chancellor for the group you are addressing, noted in the published policy.
    
    
• When using Office 365 as the sending mail service, you may specify a maximum of 500 recipients per email.
  
  • Multiple and consecutive emails at this limit could flag your email with Microsoft and Microsoft could block your email for 24 hours.
  • Microsoft may see repeat instances of this from one account over time and block the email for longer periods of time.
  • Find out more about the limits of email service in Office 365 at this web page: Exchange Online Limits
    
    
• When using Davismail as the sending mail service, please review Google's policy as well as UC Davis policy.
  • Find out more about the limits of email service in Google Workspace at this web page: Gmail Program Policies
    • Emails can be reported as spam to Google by the recipient at any time.
  • Multiple and consecutive emails at this limit could flag your email with Google and Google could suspend your email and Google Workspace account.
  • Google may see repeat instances of this from one account over time and block or suspend the email and Workspace for longer periods of time.