AutoSender keeps resending the same message and doesn’t change the status to ‘1’ (i.e. ‘sent’). What's happening ?

Most probably the mail ID field is not an integer serial value of type 'text.
The ‘id’ and ‘status’ mail fields should be of type 'text'.
The ‘id’ field should be an integer auto-enter serial value, i.e. ‘1, 2, ...’ and not something like ‘M001, M002, ...’ or ‘0001, 0002, ...’