The e-mail address is linked to a file (Candidate or Contact)
Go to 'Candidates' or 'Contacts'.
Search: "e-mail address" contains "<the e-mail address>".
Open the file that contains the e-mail address.
Erase the field E-mail addresses
The e-mail address is not linked to a file
Go to "E-mail".
Search the e-mail address at All Received.
Open the e-mail.
Click Remove E-mail address from list.