An email element in manpages will be rendered simply as plain text. That's not broken, but it could be better. There is support for email elements in *info sections, but nothing for appearance in normal text.
What happens is that the email element is actually processed by the html layer, which calls the template inline.monoseq with parameter content. But the manpages version of the inline.monoseq template does not use the parameter content, and so it simply falls back to processing the children. This could be made more consistent, and then the email element could be processed like in html in monospace with angle brackets by default.
Attached is an example document, which I processed with xsltproc /usr/share/xml/docbook/stylesheet/docbook-xsl/manpages/docbook.xsl test.xml .