Finding matching data in long columns of data

Aloha,

I have a list of guests at a hotel and I am trying to identify reservations with the same name or same e-mail address or same frequent guest account number. I need to identify reservations traveling together so I can be sure that I assign connecting or adjacent rooms (as these are likely family members traveling together with multiple reservations).

I need to program into my macro a routine that searches for matching data in a column of data - so any item in a column of which there are at least two of the same such as names or email addresses.

I am not sure where to start. I am wondering if any of you have ideas on how to accomplish this kind of search to look for and identify duplicates within the same column than to have the entire row of these matches copied to another sheet.

Mahalo,

Andrew