How do spammers typically send their messages?

Spammers typically send their messages by exploiting open mail relays. An open mail relay is a mail server that allows anyone on the internet to send emails through it, regardless of the origin or authentication. This makes it an attractive target for spammers because it provides anonymity and the ability to bypass security measures that would normally block their activities. By using these unsecured servers, spammers can flood inboxes with unsolicited messages without having to maintain their own servers or worry about getting their own domain blacklisted.

In contrast, other methods listed, such as using secure email servers or authorized corporate emails, involve legitimate, trusted communication channels that are heavily monitored for spam activity. Similarly, encrypted messages would not typically be used by spammers, as encryption adds a layer of security that is counterproductive to the mass distribution of junk mail. As a result, exploiting open mail relays becomes the most common approach for spammers to reach a wide audience while evading detection.