Hello @CFH10016 ,
If you're noticing a pattern like this with certain contacts, I'd advise unsubscribing them and deleting them from your contacts. At times, bad actors will collect other peoples' email addresses, and submit them for different organizations' emails. The problem with these is that if they're being entered manually, then the basic safeguards against things like bots (such as reCaptcha) can be easily sidestepped.
If this becomes a persistent issue, then the only viable solution would be to turn on Confirm Opt-In for your account. This way, if the owner of the email address isn't the one who submitted their contact info, they'll at least have the ability to delete / ignore the confirmation email, and avoid receiving emails from you. This will also safeguard you, to ensure you're not paying or sending to contacts that don't actually want to receive your emails.
See also:
Enabling advanced email permissions
... View more
