• Enabled (default) - Domino declares its maximum message size to connecting hosts and checks the sending host's estimates of message size before accepting transfer. If the sender indicates that a message to be transferred is larger than the maximum size, Domino returns an error indicating that it will not accept the message
• Disabled - Domino does not advertise its maximum message size or check inbound message size before transfer.

• Enabled (default) - Improves performance by allowing Domino to accept multiple SMTP commands in the same network packet.
• Disabled - Domino does not accept multiple SMTP commands in a single packet.

• Enabled - Domino supports incoming requests to return delivery status notifications to the sender for failed, delayed, delivered, and relayed messages. Domino sends delay reports for low-priority messages held until the low-priority routing time to the sender of an SMTP message upon request.
• Disabled (default) - Domino does not return delivery status notifications for SMTP messages. Domino will return failed DSNs.

• Enabled - Domino accepts 8-bit messages as is, allowing reception of unencoded multinational characters.
• Disabled (default) - Domino requires inbound messages containing 8-bit characters to be sent using 7-bit ASCII encoding.

• Enabled (default) - In response to the Help command, Domino displays a list of supported commands.
• Disabled - Domino ignores the Help command.

• Enabled - Domino accepts inbound requests to verify user names.
• Disabled (default) - Domino denies requests to verify user names.

• Enabled - Domino expands mailing lists or groups to show individual recipient names.
• Disabled (default) - Domino does not expand lists and groups.

• Enabled - Domino accepts inbound "pull" requests from other SMTP hosts to transfer messages destined for the calling server. Enabling ETRN support allows for more efficient use of bandwidth resources by allowing a remote SMTP host to request pending messages at the same time it transfers messages to the Domino server.
• Disabled (default) - Domino does not accept inbound "pull" requests from other SMTP hosts.

• Enabled - Domino supports the STARTTLS command, allowing it to create an encrypted SSL channel over the SMTP TCP/IP port.
• Required - Domino accepts inbound SMTP connections over the TCP/IP port only from hosts that issue the STARTTLS command.
• Disabled (default) - Domino does not allow secure SSL connections over the SMTP TCP/IP port.

After accepting the STARTTLS command from a remote server, Domino uses settings for the server's SSL port to govern authentication for the sessions. For Domino to authenticate remote hosts that use the SMTP AUTH command, name and password authentication must be enabled for the Domino SSL port. We'll cover how to configure the server's SSL port in part two of this article series.