I am currently being swamped with Russian spam so I followed several tutorials to create a custom filter but the last step is eluding me. My current filter looks like this:Has the words: lang:Russian OR  OR  OR  OR  OR Everything that matches the filter bypasses my inbox and gets deleted.On top of this I would like to check for this: charset=koi8-r Is this doable with Gmail's filters?
Adding rules that filter email by their content-type in Gmail
gmail;gmail filters