A number of other mail clients (AFAICT Thunderbird[1] and iOS) offer support for highlighting of addresses that fall outside the sender's domain. I'd very much appreciate a similar feature in Claws, via plugin or otherwise. 1. Thunderbird external domain highlighter https://addons.mozilla.org/de/thunderbird/addon/highlight-external-addresses/ 2. iOS mail "Mark Addresses" feature http://osxdaily.com/2017/05/08/mark-addresses-domains-mail-ios/
*** Bug 4123 has been marked as a duplicate of this bug. ***