The
EX_TEMPFAIL exit code (value 75) is returned by
sendmail to indicate that a temporary error has
occurred. Temporary errors mean that the mail message will be put in
(or remain in) the queue for the present, and another delivery
attempt will be made later.
One example of this type of error occurs in looking up aliases via a
network service, such as NIS. If all the servers are too busy to
answer before a timeout, sendmail should
temporarily queue the message and look up the aliases again later:
alias database unavailable
Another example occurs when there is a failure to open a file
descriptor as a file pointer with fdopen(3).
This can happen when caching an SMTP connection:
cannot open SMTP client channel, fd=file descriptor
In looking up hostnames with DNS, the name server or the network
might be so overloaded that the lookup will time out:
host: Name server timeout
DNS lookups can also be caused by dial-on-demand networks when the
connection is not fast enough. If the delivery mode of
sendmail is set by the
DeliveryMode option (DeliveryMode)
to defer, that failed connection is deemed
temporary.
Normally, delivery agents exit because they have finished delivering
the email. If one exits because of a received signal,
sendmail logs the following message and the
fork(2)'d child exits with an
EX_TEMPFAIL exit code:
mailer delivery agent name died with signal signal in octal
Also, if the -X command-line switch (Section 14.2) was used to specify a transcript file, the
arguments to the delivery agent will be recorded in that file.
