Dear Sir, It would be better to address him by name.
this abc, secretary of the organization. i got your reference from my senior xyz.....
Your name has been given to me by Peter Postule, with whom you worked five years ago.
He wants to know how you know him more than who you are. He can find that out by looking at the information below your signature:
cCan i I begin the letter in this manner?? (..) iIf not, then what is the most appropiate beginning line? ?