Using "mailto:" Links in SharePoint Pages
Now it is possible to add “mailto:” links in SharePoint Pages content. You can do that in text web parts by inserting a link with “mailto:”.
This is a small change and is not reflected in the Office 365 roadmap, but the comment about that has been added to the corresponding user voice request (btw, “tel:” links are still not supported).
I want to remind that you can also specify a “mailto:” link for an Image web part. Quick Links web part does not support “mailto:” links.