Topic Last Modified: 2007-05-16

Use the options on the Messages tab to configure the limits that are applied to the message size, session size, number of messages per connection, and number of recipients per message. You can also configure the options that control how undeliverable messages are handled. The following options are available on the Messages tab.

Limit message size to (KB)

Select this check box to limit the message size for this SMTP virtual server. To allow unlimited maximum message size, clear the check box. The SMTP virtual server will advertise this value as the maximum message size that this SMTP virtual server accepts. If a mail client sends a message that exceeds the limit, the client will receive an error. If a remote server supports EHLO, it will detect the advertised Maximum message size value when it connects to the SMTP virtual server and won't even try to deliver a message that exceeds the limit. Instead, the message is returned to the sender with a non-delivery report (NDR). A remote server that doesn't support EHLO will try to send a message that exceeds the size limit and send an NDR to the sender when the message doesn't go through.

For the Limit message size to (KB), type a value for the maximum size of a message, in kilobytes (KB). The default value is 2,048 KB. The minimum value is 1 KB.

Limit session size to (KB)

Select this check box to limit the maximum amount of data that is accepted during the total connection. This value is the sum of all messages sent during the connection (applying to the message body only).

Type a value larger than the Limit message size to (KB) value. Set this maximum carefully, because the connecting message transfer agent (MTA) is likely to resubmit the message repeatedly. The default size is 10,240 KB. The minimum value is equal to the value that is assigned to the individual message size limit.

Limit number of messages per connection to

Select this check box to limit the number of messages sent in a single connection. The default value is 20. This feature also provides a method to increase system performance by using multiple connections to deliver messages to a remote domain. Therefore, after the set limit is reached, a new connection is automatically opened and the transmission continues until all messages are delivered. To disable this feature and have no limit, clear the check box.

Limit number of recipients per message to

Select this check box to limit the maximum number of recipients for a single message. The default value is 100, which is the minimum required number that is specified in Request for Comments (RFC) 2821. To disable this feature and have no limit, clear the check box.

After an error message is received, some clients return messages together with an NDR that indicates that the maximum number of recipients has been exceeded. A server that is running Windows Server 2008 SMTP Server does not return messages together with an NDR in this instance. It opens a new connection immediately and processes the remaining recipients. For example, if the recipient limit is set to 100 and a message that has 105 recipients is being transmitted, the first 100 recipients are delivered in one connection after receipt of the error message. Then a new connection is opened and the message is processed for the remaining five recipients.

Send copy of Non-Delivery Report to

When a message is undeliverable, it is returned to the sender with an NDR. You can designate that copies of the NDR are sent to a specific SMTP mailbox. Type an e-mail address for the mailbox.

Badmail directory

All NDRs follow the same delivery process as other messages, including attempts to resend the message. If the NDR has reached the retry limit and cannot be delivered to the sender, a copy of the message is put in the Badmail directory. Messages that are put in the Badmail directory cannot be delivered or returned. Check the directory regularly and reconcile the messages, because a full directory may adversely affect SMTP Server performance. By default, the Badmail directory is a subfolder of your Mailroot directory. To select an alternative location for the Badmail directory, click Browse.