Allow the plus symbol in email addresses

Edit : did you change your posting ? i did not read the contact form widget at all.
i do not have a widget that way. – but you can have a html widget and insert contact form shortcodes to it.

this is checked in the concerning js file : contact.js line 118 (Enfold 5) with a regex: (is_special_email)
if( ! value.match( /^[a-zA-Z0-9.!#$%&'*+\-\/=?^_{|}~ÄÖÜäöü]+@\w[\w\.\-ÄÖÜäöü]*\.[a-zA-Z]{2,20}$/ ) )
`

so if needed take the corresponding email input field with special characters and german Umlaute (äöüÄÖÜ):