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.
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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.
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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
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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.
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