The tutorial LaTeX/Hyperlinks shows that the following should be compilable.
\documentclass{article}
\usepackage{hyperref}
\begin{document}
\href{mailto:a_b@c.def}{a_b@c.def}
\end{document}
However, I cannot compile it. Is it necessary to escape underscores in \href with a pair of $s or \?
Note that escaping the underscores with a pair of $ does not make sense in the above context, of course!

