While there will be instances where HerbMail identifies a visitor who subsequently submits their email via form, we minimize these occurrences by setting a threshold on the site visit time before we identify the visitor. There is an added delay of approximately one minute, after this threshold is met, before the identified visitor is synced into your system, giving further opportunity for the visitor to complete a form on their own.
Herbmail will not provide you with emails that are already in your system, which are identified either by our native integration (i.e. Klaviyo, Iterable) or a suppression list that you upload. There will, of course, be occasional instances where a visitor provides their email on their own even after the threshold and subsequent delay, and this expected overlap is baked into our pricing.