We’ll let the experts explain this one.
Visit Microsofts's Create a group in Outlook and Add and remove group members in Outlook pages for more information.
- Office 365 imposes a Message Recipient limit of 500 recipients for distribution lists. This is the maximum number of recipients allowed in the To, Cc, and Bcc fields for a single email.
- If you need to send a message to more than 500 recipients, a Sympa distribution list should be used to send the email. When an email is sent to a Sympa list, Office 365 interprets the recipient limit as one recipient even though the list could include thousands of email addresses.
- The Outlook web client only allows one address to be added to a Contact List at a time; you can't paste a list of addresses into a Contact List. You can paste a list of addresses into an Outlook desktop Contact Group.
- If you are copying and pasting an email list into a contact group from Word or Excel, please use column format.