XFOR: SMTP Message to More Than 100 Recipients Is Not Delivered

• Microsoft Exchange Server version 5.0

SYMPTOMS

If you send a Simple Mail Transfer Protocol (SMTP) message through the Internet Mail Service to more than 100 recipients, the message may not be delivered.

CAUSE

The Request For Comments (RFC) 821 specification limits the number of recipients for a single message to a maximum of 100. When an SMTP server that supports RFC 821 receives a message with more than 100 recipients, it requests that the sending system send the original message so that it can be separated into multiple messages, each with 100 or fewer recipients. The Internet Mail Service does not properly respond to this request.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0. This problem has been corrected in the latest U.S. Service Pack for Microsoft Exchange Server version 5.0. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces): S E R V P A C K

MORE INFORMATION

When an SMTP server receives a message, it stores the recipients in a buffer until all the recipients are processed. When the buffer reaches 100 recipients on an SMTP server that supports RFC 821, the server sends a return code of 522. This return code indicates that the sending system should send the message text before continuing to send recipients. This allows the server to create multiple messages, each with 100 or fewer recipients.

Under these circumstances, the Internet Mail Service does not respond to this return code properly. It continues to send recipients instead of sending the message text first.