Define the \mailheader macro and document conventions for using it.
diff --git a/Doc/texinputs/python.sty b/Doc/texinputs/python.sty
index 498fc3b..6b892cb 100644
--- a/Doc/texinputs/python.sty
+++ b/Doc/texinputs/python.sty
@@ -833,6 +833,7 @@
\newcommand{\ctype}[1]{\texttt{#1}} % C struct or typedef name
\newcommand{\cdata}[1]{\texttt{#1}} % C variable, typically global
+\newcommand{\mailheader}[1]{\texttt{#1}}
\newcommand{\mimetype}[1]{{\small\textsf{#1}}}
% The \! is a "negative thin space" in math mode.
\newcommand{\regexp}[1]{%