He's not necessarily saying that "while they are making payments" but he wants the emails somehow, and he said that the website is https.
What could be understood from this ?
1. Well, first, since it's https, you cannot (easily) sniff the communication in a network between a client/user/computer/IP and a server/website/service, because it's encrypted, that
s from https, stands for secure
secured hypertext transfer protocol. In other words, this means that if you go to the mall, connect to a public wi-fi network, a hacker wouldn't be able to (easily) grab your email address, while you login, make a payment, reset a password, etc ... (while it's very easy to do it for a non secure website, http) but it's still possible, if you "like computers".
2. The OP is thinking that somebody could get the emails by different means, such as hacking the database server, or at least getting at the database through other means.
Indeed, this is illegal OP, and it's not accepted on this forum. You should read the forum rules. I'm pretty sure that you know that there's no other way of getting those, than using something that is not very ethical