Send an email using triggers to contacts related to the accounts when account is updated. If 2 contacts has same email than send only 1 mail to that contacts having similar emails. In the email body mention the name of contacts having similar emails in a tabular format. For example if the Account A1 has 5 contacts c1, c2, c3, c4, c5 and c1, c2, c3 has similar emails and other having unique email than the names of the contact should be show in the table in the email body of the contacts having similar emails.

Send an email using triggers to contacts related to the accounts when account is updated. If 2 contacts has same email than send only 1 mail to that contacts having similar emails. In the email body mention the name of contacts having similar emails in a tabular format. For example if the Account A1 has 5 contacts c1, c2, c3, c4, c5 and c1, c2, c3 has similar emails and other having unique email than the names of the contact should be show in the table in the email body of the contacts having similar emails.