[\w-]+(?:\.[\w-]+)*@(?:[\w-]+\.)+[a-zA-Z]{2,7}

/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*$/i

\b[A-Z0-9._%-]+@[A-Z0-9-]+\.[A-Z]{2,4}\b

(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]) 
\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)
\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)
\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])

 \b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)
 \.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)
 \.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)
 \.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b