Title Case
^[A-Z][a-z@./'\\]*([ \-][A-Z][a-z@./'\\]*)*$
Upper or Title Case
^[A-Z][A-Za-z@./'\\]*([ \-][A-Z][A-Za-z@./'\\]*)*$
^[A-Z][A-Za-z.']*([ /@\-\\][A-Z][A-Za-z.']*)*$
^[A-Z][A-Za-z.]*([ .'/@\-/][A-Z][A-Za-z]*)*$
Upper or Title Case or Empty
^[A-Z][A-Za-z.']*([ /@\-\\][A-Z][A-Za-z.']*)*$|^$
^[A-Z][A-Za-z.]*([ .'/@\-/][A-Z][A-Za-z]*)*$|^$
Email Address:
^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$
^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\\.([a-zA-Z]{2,5})$
Email Address: (without % or \\%)
^[a-zA-Z0-9\\.\\!#$&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\\.([a-zA-Z]{2,5})$
References