That file is a vCard which stores your sender information - essentially an online business card which people can use to add you to their safe senders right away! This makes it far easier for your next emails to be delivered straight to their inbox.
¿Can I remove the vCard from my opt-in emails?
No, and that's a good thing! Major ISPs (such as Gmail, Outlook.c om and Yahoo) just love to see folks adding you to their safe senders! A vCard is t he perfect way to do this, helping you keep your deliverability in good shape :)