mailto:email@example.com is not accepted by URL type properties, but should be.
There're a property for email https://www.wikidata.org/wiki/Property:P968, which is unused https://www.wikidata.org/w/index.php?title=Special%3AWhatLinksHere&target=Property%3AP968&namespace=0 because of this. As arbitrary access is coming, we need to fix it as we can use it in Wikivoyage.
Change 193669 had a related patch set uploaded (by Gerrit Patch Uploader):
Add mailto to the allowed URL schemas In I86cff20, Thiemo Mättig (WMDE) says: "Please note that I currently don't want to add mailto by default, mainly for privacy reasons."