Just to add my tuppence worth, again I’ll add my weight to what they guys say and shout about how Zapier is awesome. Some of our clients also use a free version of Zoho CRM which Unbounce has integrations for and we also have some clients on Salesforce who I coded custom web hooks for. Others just get it via email or again spreadsheets., tbh most clients just want an email fired off but we do try to push CRM systems as they give you a much better chance at reporting and proper customer management.
If you’re not using a CRM, I seriously recommend grabbing a free Zoho account just to have somewhere for your leads to live, if you already have a CRM, then I’m sure between us all we can advise on how to integrate Unbounce to get your leads drop straight into there. 