sendmail, 4th Edition

FallBackSmartHost

Fallback SmartHost V8.13 and later

At sites with poor (connect-on-demand) or unreliable network connections, SMTP connections can often fail. In such situations, it might not be desirable for each workstation to queue mail locally for later delivery attempts. Prior to V8.13 sendmail, the FallbackMXhost option (FallbackMXhost on page 1030) was used to provide a final, alternative method for getting a message out the door by specifying the name of a mail exchanger machine (MX record) of last resort.

The trouble with this strategy is that the FallbackMXhost option works only if the recipient’s hostname can be looked up in the first place. If the hostname cannot be found, not even the FallbackMXhost is tried.

For most well-managed sites, this is not a problem. Machines can still look up hosts on the Internet, even if they are on an internal business LAN or behind a firewall. But not all sites are well managed, and some sites disallow external lookups as a matter of policy. For such sites, the FallbackMXhost option will not do.

Beginning with V8.13, the FallBackSmartHost option has been added to solve this particular problem. Even if the recipient’s host cannot be found, the fallback host specified with this new option will still be tried.

The FallBackSmartHost option is declared like this:

O FallBackSmartHost=host.domain                 ← config file (V8.13 and later)
-OFallBackSmartHost=host.domain                 ← command line (V8.13 and later)
define(`confFALLBACK_SMARTHOST', `host.domain') ← mc config ...