PMDF System Manager's Guide

The identnone keyword enables IP to hostname translation, and both IP number and hostname will be included in the Received: header for the message. The identnonesymbolic keyword enables IP to hostname translation; only the hostname will be included in the Received: header for the message. The identnonenumeric keyword inhibits the usual DNS reverse lookup translation of IP number to hostname, and may therefore result in a performance improvement at the cost of less user-friendly information in the Received: headers. identnone is the default.

The identnonelimited keyword has the same effect as identnone , as far as reverse DNS lookups, and information displayed in Received: header lines. Where they differ is that with identnonelimited the IP literal address is always used as the sole basis for any channel switching due to use of the switchchannel keyword, regardless of whether the DNS reverse lookup succeeds in determining a host name. Note that since channel switching is always performed preferentially based on IP address rather than host name, the effect of identnonelimited is merely to disable ever trying host name switching in case all IP address rewriting failed.

Keyword	DNS	IP address	Reverse hostname	Fall back to
	reverse	in Received:	in Received:	hostname
	lookup	header line	header line	channel switch
identnone	Yes	Yes	Yes	Yes
identnonelimited	Yes	Yes	Yes	No
identnonenumeric	No	Yes	No	No
identnonesymbolic	Yes	No	Yes	Yes

The forwardchecknone , forwardchecktag , and forwardcheckdelete channel keywords can modify the effects of doing reverse lookups, controlling whether PMDF does a forward lookup of an IP name found via a DNS reverse lookup, and if such forward lookups are requested what PMDF does in case the forward lookup of the IP name does not match the original IP number of the connection. The forwardchecknone keyword is the default, and means that no forward lookup is done. The forwardchecktag keyword tells PMDF to do a forward lookup after each reverse lookup and to tag the IP name with an asterisk, * , if the number found via the forward lookup does not match that of the original connection. The forwardcheckdelete keyword tells PMDF to do a forward lookup after each reverse lookup and to ignore (delete) the reverse lookup returned name if the forward lookup of that name does not match the original connection IP address, and stick with the original IP address instead. (Note that having the forward lookup not match the original IP address is normal at many sites, where a more "generic" IP name is used for several different IP addresses.)

These keywords are only useful on SMTP channels that run over TCP/IP.