Rocket Validator automatically checks your pages on the W3C Validator.
HTML issues tagged as mailto.
<a> tags can be used to link to an email address using the
mailto protocol in the
href attribute. Ensure that there is no space in the email address.
<a href="mailto: email@example.com">This is wrong as it contains an space</a> <a href="mailto:firstname.lastname@example.org">This is OK</a>
When was the last time you validated your whole site?
Keep your sites healthy checking for A11Y/HTML issues on an automated schedule.