Multiple RHS mailertable entries

It is possible to specify a colon-separated list of MX records, hosts, or IP addresses in the right-hand side (RHS) of the sendmail mailertable database to create "private" MX records. Each MX record, host, or IP address is tried in left-to-right order.

Examples:    esmtp:MX_record_1:MX_record_2    esmtp:[host1]:[host2]    esmtp:[]:[]

This behavior is documented in doc/op/op.*:

5.1.2. The right hand side

       If the mailer is the built-in IPC mailer, the host may be a colon-separated list of hosts that are searched in order for the first working address (exactly like MX records).

5.1.5. IPC mailers

       The host name passed in after the “$@” may also be a colon-separated list of hosts. Each is separately MX expanded and the results are concatenated to make (essentially) one long MX list. The intent here is to create “fake” MX records that are not published in DNS for private internal networks.

More information:
Link 1
Link 2

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Last modified: 2006/11/27