Looking at Apple's Mail: Show detailed message headers, it sounds like I shouldn't be seeing Resent-from headers, because I have the View->Show message headers preference set to "Default."
The support page sounds like I should need to use Custom to ever see Resent-from.
How can I turn off the Resent-from header?
I also tried setting the preference to Custom… without adding any headers at all, and nothing changed.
My Mac is running OS X 10.10.5, Yosemite.
Best Answer
Visit https://support.apple.com/kb/PH19118?locale=en_US The following reads:
When you view messages, you can show more fields in the message header, such as List-ID or Resent-From. Show the headers: Choose Mail > Preferences, click Viewing, then select “Show additional message headers.”
Change the headers that are shown: Click Select Headers. To delete a field, select it, then click Remove . To add a field, click Add , then enter a field name.