To prevent potential spam attacks, OU emails are limited to 500 recipients per email. When attempting to send an email to more than 500 recipients, users may receive the following non-delivery report from Microsoft:
Too many recipients in the message. Reduce number of recipients in message and resend.
This limitation is enforced by Microsoft and OU IT is unable to change or increase recipient limitations. If you need to send an email to more than 500 recipients, you may request a distribution list or a listserv. For more information about distribution list and listservs, please visit the Service Catalog.