DOVER, Del. - Authorities in Dover, Delaware are warning residents following a number of reported thefts from post office collection boxes.Within the last three weeks, police say they have received at least eight reports of thefts where suspects removed mail from United States Postal Service mailboxes.Police say once the suspects have removed the mail, they remove any valuables from the envelopes, including checks.In some cases, suspects have been able to alter or change checks to receive the money themselves.The Dover Police Department cited one case in which a suspect was able to fraudulently acquire $40,000.The incidents remain under investigation and police say two Dover locations have been confirmed as being targeted.