[NAME, COMPANY AND ADDRESS, ex.
John Smith
XYZ Inc.
1234 First Street
Suite 567
Anycity, Anystate  85245]
 

Dear [NAME, ex. John Smith], 

We were delighted to hear the wonderful news about your newly-born [son / daughter]!  I'm certain the new addition to your family will bring you much happiness and enjoyment, not to mention several sleepless nights. Let me know if there is anything I can do to assist here at the office.

Please give my best to your family; I look forward to meeting [NAME, ex. Corey]. 

Best regards,

[YOUR NAME, ex. Jill Jones]