Heh sorry about not being clear enough. I meant the id of the form instance, or submission.
Every submission gets an ID in the database of CF7, so I would like to include that ID in the outgoing emails.
So for instance, when I make the first submission, I would get an email that informs me my message has an ID number 1.
The plugin Contact Form to DB Extension clearly outputs all submissions in a table, so I guess there should be a way to output some form of an ID.
Basically, keeping track of all submissions - if the person in charge gets, for instance emails with submissions 123467, then he/she automatically knows something's wrong since the submission 5 wasn't delivered.