@mahescho said in Rules:
Is there a way to filter arbitrary headers?
Yes, that’s exactly one of the purposes it was designed for.
List-Id: <pgsql-hackers.lists.post.org>as search criteria in a transport-message-header-rule, will target mail-items with the corresponding “List-ID”-header. Consider the matching algorithm a case-insensitive fulltext-search on the entire header-section.
As of current, the searchable length of message-headers is limited by kopano-server. Particulary, gmail tends to create very long transport-headers, that by chance get truncated. As a mailing-listid headertag is regularly located at the lower end of the header-section, the filter-rule might fail in this case.