For each email sweden expose telegram that “knocks” on the door of the servers operating in the management of incoming mail, checks are performed on multiple levels , in order to allow entry only to reliable communications, avoiding that the boxes are submerged by “junk” mail. Even before an email is subjected to the screening of the actual anti-spam filter, a check is performed on:
the sender's email domain , to check if it is registered and active;
the existence of the recipient's mailbox;
the reverse DNS of the IP of the server from which the sender sends: each “clean” IP has its own reverse (rDNS), that is, a hostname to which it responds, and if this is not present, the IP is probably malicious.
blacklisted domain or server with blacklisted IP : If the sender sends from a server with a blacklisted IP, communications sent from it are unlikely to be reliable.
