The host part of the named contact address is not known or not globally routables, such as localhost(.localdomain).
For more information please consult:
The tag is present in Lintian version
That is the most recent version we know about.
We use semantic versions.
The patch number is a commit step indicator relative to the
release tag in our Git
You can find the detection logic for this version at commit ca97c3a. For merge requests, please use the latest version in the Lintian check fields/mail-address.