Is it possible to recall an email that was not opened after a mailing?

No. There are functions on mail Exchange servers and lab options on Gmail that allow to cancel a mailing. However, that procedure must be completed excessively quickly.
Since PUBLITRAC users do not have a direct access to the email box, the time required to contact PUBLITRAC and the account manager to access this box and complete that procedure
would make the functionality impossible to use.