In Microsoft Office 365 dedicated, you receive a non-delivery report (NDR) when you send an email message to many recipients. The NDR contains an error that resembles the following:
5.5.3 - Too many recipients in the message. Reduce number of recipients in message and resend.
The total number of recipients of an email message exceeded one of the following recipient limits:
Organizational recipient limit: These limits apply to all servers that are running Microsoft Exchange Server 2010 and Microsoft Exchange Server 2007 in the organization.
Connector recipient limit: These limits apply to any messages that use the specified Send/Receive connector.
Server recipient limit: These limits apply to a specific Hub Transport server or Edge Transport server.
User recipient limit: These limits apply to a specific user object, such as a mailbox, contact, distribution group, or public folder.
This resolution is customized for Office 365 dedicated (O365-d), although aspects of this resolution might be applicable in other contexts.
By default, the organizational recipient limit is 5,000 recipients. However, this limit may vary in your organization. Additionally, a given user may be configured for a lower recipient limit. Generally, if a user receives the NDR that is mentioned in the "Symptoms" section, please advise the user to reduce the number of recipients and to resend the message.
Note Exchange Server 2010 treats a distribution group as one recipient. If a message must be sent to lots of recipients, consider creating a distribution list for this task.
If you feel that the NDR was received in error, or you have to request a change for a given user’s recipient limit, please escalate this issue to Microsoft Online Services Support for review. To do this, please use the Exchange Online topic and the Mail Routing sub-topic when you submit a support incident online to Microsoft Online Services Support, or contact Microsoft Online Services Support by telephone, and make sure that the following information is included.
A copy of the NDR that was received
The SMTP of the sender
Subject, Date, and Time of the message
Note Although Microsoft Online Services Support may change a user’s recipient limit, any changes to the organizational, connector, or server recipient limit requires that your company's Service Delivery Manager (SDM) file a Change Request.