IMTA interprets the contents of header lines only when necessary. However, all registered headers containing addresses must be parsed in order to rewrite and eliminate shortform addresses and otherwise convert them to legal addresses. During this process, comments (strings enclosed in parentheses) are extracted and may optionally be modified or excluded when the header line is rebuilt.
This behavior is controlled by the use of the commentinc, commentomit, commentstrip, and commenttotal keywords. commentinc tells IMTA to retain comments in header lines. It is the default. commentomit tells IMTA to remove any comments from addressing headers, for example, To:, From:, or Cc: headers.
commenttotal tells IMTA to remove any comments from all headers, including Received: headers; as such, this keyword is not normally useful or recommended. commentstrip tells IMTA to strip any non-atomic characters from all comment fields. These keywords can be applied to any channel.