Merge branch 'ag/doc-send-email'

Documentation updates for "git send-email". * ag/doc-send-email: docs: mention possible options for Proton Mail users docs: add a paragraph explaining the `sendmailCmd` option of sendemail docs: add an OAuth2.0 credential helper for AOL accounts docs: add outlookidfix config option to sendemail documentation docs: link OpenSSL's verify(1) manual page to know about -CAfile and -CApath options