I have a list of potential customers.

some data are missing or other may be out of date.

What would be the best pratice from a technical point of view to ask each member of the list to update its own data, so that it automatically updates the corresponding fiels?

I am thinking of a mass mailing but I cannot figure out how to share the data thru the email and ask for the updating process.

Or will this be achieved solely by asking the customers to access the portal (i am not familiar with this portal module)?