HP-UX Mailing Services Administrator's Guide (B2355-91064)

FallbackMXhost=fallbackhost
The FallbackMXhost option works only if Sendmail can look up the host name of
the recipient. If it does not find the host name, the FallbackMXhost is not useful. In
such situations, Sendmail uses the FallBackSmartHost option.
The FallBackSmartHost option specifies the name of an MX record that Sendmail
must use as the last resort if the MX records are not available to identify the remote
host. This option is given a low priority so that Sendmail tries to connect to it only if
all other attempts to connect to the remote host fail.
Following is the format for the FallBackSmartHost option:
FallBackSmartHost=hostname
Where: hostname specifies the canonical name to which the host falls back.
The mail message forwarded to that host name fails if hostname is an empty string
or is the name of a nonexistent host. You can also use macros to represent the hostname.
Sendmail expands these macros before connecting to the remote host. If the hostname
that you specify for the FallBackSmartHost option exists in the $=w class, Sendmail
silently ignores the hostname.
The FallBackSmartHost option is also useful for unreliable FallbackMXhost
servers. When a FallbackMXhost server goes down, Sendmail uses the
FallBackSmartHost option to sustain the flow of mail messages.
You must be careful while using the FallBackSmartHost option, because Sendmail
can relinquish its special privileges if you specify this option from the command line.
The FastSplit Option
You can use the FastSplit option to suppress MX lookups before splitting an envelope
and also to limit the number of envelopes that can be delivered on the initial attempt.
Following is the syntax for the FastSplit option:
-OFastSplit=num
Where: num is of type numeric.
If num is a negative non-numeric value or zero, Sendmail enforces initial sorting based
on the MX records.
If num is set to a value greater than zero, the initial MX lookups on addresses are
suppressed during sorting. This can result in faster envelope splitting. If the mail is
submitted directly from the command line, the value also limits the number of processes
that deliver the envelopes.
When Sendmail expands an alias, such as when using aliases to send a mail to a mailing
list, it sorts the list of new recipients by host. Normally, the list of hosts is sorted by
MX records rather than by the host name. After sorting, Sendmail splits the new
MX-sorted list into multiple envelopes.
Modifying the Default Sendmail Configuration File 47