I'm breaking my head. I searched the internet for hours but it seems there is no mention of this elswhere.
About a year ago, my boss created a form. Based on a submission, several mails are send. It happens that people complain they didn't receive an email. Most of the time this is because they made a typo in there email address. But know, i'm looking deeper in to this and i find that for a lot of entries, there are no values stored, only a hyphen.
The form has 1730 submissions, in 517 of them there is only a hyphen in 3 fields (address, phone, e-mail). The fields "name" and" firstname" are always correct. All fields are just text fields with no limitations set. I can't find any relation. This happens totally ad random.