Local host alias Option

The  channel option is used to specify an alternate name for the MTA system itself. Normally, the local host system is known by the name that appears as the   on the   channel. But it is sometimes useful for the local host to have different names depending on the channel being used. This situation usually arises when a machine is connected to more than one network. For example, a system may need to be known as ymir.uucp on the UUCP network, ymir.claremont.edu on the Internet, and ymir.bitnet on BITNET.

If  is specified, it is communicated as the local host&#x27;s name to any remote hosts with which this channel communicates. This alias will replace the local host&#x27;s name wherever it appears in the envelope and header of messages queued to the associated channel. If this alias is omitted the local host&#x27;s official name (that is, the official host name associated with the  channel,  ) is used.

In legacy configuration, a local host alias is specified by placing it on the second line of a channel definition, subsequent to the official host name: channel-name ...keywords... official-host-name local-host-alias The local host alias only affects the name of the local host. No other system names are affected. The effects of the local host alias are strictly limited to the channel to which the alias applies.

A  on the SMTP server channel (typically  ) overrides the TCP/IP stack&#x27;s official host name for use on the SMTP server&#x27;s 220 banner line. (If the TCP/IP stack doesn&#x27;t have a value for some reason, we finally fall through to the   from the    channel.)  A    on an outgoing   channel overrides the TCP/IP stack&#x27;s official host name for use on the EHLO/HELO/LHLO line. As of iMS 5.2, the new-in-that-version   TCP/IP-channel-specific option takes precedence over the   (in both directions, server and client).

Note: The use of local host aliases is discouraged. If at all possible, each system should be known by one and only one name on all networks. Networks should strive to make this a reality. (Back when Internet vs. UUCP vs. BITNET names were an issue, when it was impossible for a host to have the same name on both BITNET and the Internet, local host aliases were a necessary feature.  Since different networks are always  associated with different channels, a per-channel local host alias was an ideal way to give the local host a per-network name.) Note especially that when a single network is involved, it may appear that local host aliases can solve lots of problems, but often the end result is a worse mess than if the proper course of action is selected --- pick a single name and stick to it, living with the consequences of the conversion now instead of putting them off until it becomes even more difficult.

See also:
 * official_host_name Option
 * BANNER_HOST
 * Channels
 * Host name channel options