With the name of the list being LIST_NAME, you must go to the address https://lists.espiv.net/cgi-bin/mailman/listinfo/LIST_NAME and at the bottom you will find “To unsubscribe from LIST_NAME, get a password reminder, or change your subscription options enter your subscription email address:” (if the list has greek as a default language you will see “Για να διαγραφείτε απο μέλος της LIST_NAME, να δεχθείτε μια υπενθύμιση του κωδικού πρόσβασης,ή να αλλάξετε τις επιλογές της εγγραφής σας , εισάγετε την διεύθυνση email της εγγραφής σας”) fill in your listed email and click the “Unsubscribe or edit options” button. In the next page you will...

Assuming that the list’s name is LIST_NAME, go here https://lists.espiv.net/cgi-bin/mailman/listinfo/LIST_NAME and at the bottom you will see “To unsubscribe from LIST_NAME, get a password reminder, or change your subscription options enter your subscription email address:” Enter your email that registered the mailing list and click the button. Finally, on the next page click the “Remind” button. If you have forgotten the list’s admin password, fill in the bug report form  https://espiv.net/bug_report/