The official host name for a channel (second line of the channel definition block) is limited to 128 octets in length. If you are trying to use a longer official host name on a channel, shorten it to a place holder name, and then use a rewrite rule to match the longer name to the short official host name. You may see this scenario if you work with the l (local) channel host name. For example:
Original l Channel: !delivery channel to local /var/mail store l subdirs 20 viaaliasrequired maxjobs 7 pool LOCAL_POOL walleroo.pocofronitas.thisnameismuchtoolongandreallymakesnosensebutitisan example.monkey.gorilla.orangutan.antidisestablismentarianism.newt.salaman der.lizard.gecko.komododragon.com Create Place Holder: !delivery channel to local /var/mail store l subdirs 20 viaaliasrequired maxjobs 7 pool LOCAL_POOL newt Create Rewrite Rule: newt.salamander.lizard.gecko.komododragon.com $U%$D@newt
Note that when using the l (local) channel, you will need to use a REVERSE mapping table. Refer to the MTA configuration chapter in the Sun Java System Messaging Server Administration Reference for information on usage and syntax.
Certain syntax errors earlier in the MTA configuration file (for example, an extraneous blank line in the rewrite rules) may cause the MTA to wrongly interpret something as a channel definition. This could result in an intended rewrite rule being interpreted as an official host name. Besides checking the indicated line of the configuration file, also check above that line for other syntax errors. In particular, if the line on which the MTA issues this error is intended as a rewrite rule, be sure to check for extraneous blank lines above it.