Jacob is worried about sniffing attacks and wants to protect his SMTP transmissions from this attack. What can he do to accomplish this?

An SSL certificate enables TLS encryption on SMTP connections (via SMTPS on port 465 or STARTTLS on port 587), wrapping the plaintext email data in an encrypted tunnel so that any intercepted packets are unreadable to an attacker. This directly counters sniffing attacks, which rely on capturing and reading unencrypted plaintext from network traffic.

A proxy server relays traffic on behalf of clients but does not encrypt the underlying SMTP session, leaving the data readable to a sniffer positioned between any hop in the path.

EFS (Encrypting File System) encrypts files stored on an NTFS disk volume and has no effect on data actively transmitted across a network.

A firewall enforces traffic rules by allowing or blocking connections but does not encrypt permitted traffic, so SMTP data that passes the firewall remains visible to a sniffer.