Advanced SMTP Configuration

Advanced SMTP Configuration defines advanced settings for the SMTP protocol including MX resolution mail delivery. These options are accessed from Configuration > SMTP Configuration > Advanced.  

Buffer Size
The buffer size field defines the size of CMail's message buffer in Kilobytes. This should be left at 4K.

Socket Timeout
This field defines the amount of time in seconds CMail will attempt to open a connection with a remote SMTP server before reporting a timeout failure. The default value is 30 seconds although this should be modified to between 45-60 seconds if you are connected to the Internet on a very slow modem link.

Max incoming size
This field defines the largest message size that CMail Server will handle on incoming SMTP mail.

Enable MX Resolution
Up until version 2.3, CMail Server relied on an upstream SMTP mail server to look up mail records (MX records) which contain information about the location of mail servers on the Internet which handle mail for the domain you are trying to send mail to. Enabling MX Resolution means that CMail will perform this record lookup on its own, without the need for an upstream mail server.

  1. To enable this feature, check the Use MX Resolution to send mail checkbox.

Fallback to SMTP host if MX fails
This feature is used in conjunction with the MX Resolution part of CMail. If CMail is unable to obtain an answer to an MX query, it send a delivery failure notice back to the sender of the email in question. With Fallback enabled, CMail will pass the message to the SMTP server you entered in the SMTP hostname field for delivery. Note: you must have an entry in the SMTP Hostname for this feature to work correctly.

Outbound SMTP Port
Specifies the port number CMail Server will attempt to which CMail Server will send SMTP mail on a remote mail server. This should only be changed when CMail Server is used as a gateway mail server.

Refuse message if user unknown
If this option is enabled, CMail will not accept messages for unknown email addresses. If a local client attempts to send a message to an unknown recipient, delivery will be refused outright. If an external source emails an unknown username, CMail will refuse delivery and return a message to sender with to inform them that the message could not be delivered.

Assume recipient address external
Should the Refuse message if user unknown and Assume recipient address external options both be enabled, CMail will assume that the message is for an external recipient and place the mail into the outgoing queue. 

Basic SMTP Configuration
Configuration Menu
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