Set Message Size Limits

Two message size limit settings are available. Limit message size to is the value SMTP Service will display as the maximum message size this SMTP virtual server will send. If a mail client submits a message that exceeds the limit, they will get an error.

Note   If a remote server supports Extended Simple Mail Transfer Protocol (ESMTP), it will detect the advertised maximum message size value when it connects to the SMTP virtual server and won't attempt to deliver any messages that exceed the limit. Instead the remote server will simply send an NDR to the sender of an oversized message. A remote server that doesn't support ESMTP will try to send a message that exceeds the size limit, but will still end up sending an NDR to the sender when the message doesn't go through.

Limit session size to is the maximum amount of data accepted during the total connection. This limit is equal to the sum of all messages sent during the connection (applying to the message body only).

To set message size limits:

1. Start System Manager
   On the Start menu, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Navigate to the SMTP virtual server.
   1. Servers
   2. Server
   3. Protocols
   4. SMTP
   5. SMTP virtual servers
   6. SMTP virtual server
3. Right-click the SMTP virtual server, and then click Properties.
4. On the Messages tab, select the Limit message size to (KB) check box.
5. Type a value (in kilobytes) for the maximum size of a message. The default is 4096 KB. The minimum value is 1 KB.
6. In Limit session size to (KB), type a value to indicate the maximum total size (in kilobytes) of all messages in a given connection.

   The message size limit should always be be larger than the maximum message size and should be set carefully, because the connecting message transfer agent (MTA) is likely to resubmit the message repeatedly. The default size is 10240 KB. This value should be greater than or equal to the value entered for Limit message size to.

Note   Message size limits set on the SMTP virtual server apply to incoming messages. Message size 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.

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