You can determine the maximum number of recipients for a single
message sent in one connection. Some clients return messages with
an NDR, indicating that the maximum number of recipients has been
exceeded. Exchange does not return messages in this instance.
Instead it opens a new connection immediately and processes the
remaining recipients. For example, if the recipient limit is set to
1,000 and a message with 1,050 recipients is received, the first
1,000 are delivered in one connection. Then a new connection is
opened and the message is processed for the remaining fifty
recipients.
Right-click the SMTP virtual server, and then click
Properties.
On the Messages tab, in Limit number of recipients
per message to, type a number to represent the recipient
limit.
Note Recipient limits set on
the SMTP virtual server apply to incoming messages. Some recipient
limits can also be set globally on all user mailboxes and
individually on specific mailboxes. Mailbox limits can apply to
both incoming and outgoing messages.