Lastresort Channel Option

Specify a last resort host for delivery
The  channel option is used to specify a host to which to connect when all other connection attempts fail. In effect this acts as an MX record of last resort. This is only useful on SMTP over TCP/IP channels.

Note that the  host is attempted only for hosts that are in the DNS, having either MX records or an A record, and for whom the connection attempts to all the MX records -- or to the A record, if there were no MX records---have encountered temporary connection failures. (In particular, the  host will not be attempted for a host that is only in the hosts file, not in the DNS at all. Also keep in mind that a permanent 5xx error in response to a connection attempt to a host is a permanent error, and will result in bouncing a message; in particular, the   host will not be attempted after such a permanent rejection error.   Also, the   host will not be attempted if a connection succeeds, but the MTA&#x27;s wait for an SMTP banner line to be returned times out; that again is not a temporary connection failure.)

This channel option requires a single parameter specifying the name of the "system of last resort".

See also the   mapping table,  which can provide an alternate way of doing "fail over" for outbound IP connections for SMTP and LMTP channels.

Note that in most cases, it is preferable to fix problematic DNS records rather than to use ;   is intended merely for a few, special sorts of cases where correcting DNS records may not be possible, yet some "last ditch", MX-like, re-routing may be useful.

See also:
 * TCPIP channels
 * MX_ACCESS mapping table
 * IP_ACCESS mapping table
 * TCPIP connections and DNS lookups channel options
 * Gateway or firewall or mailhub channel options
 * Channel options