Step 1: Split email into sending and reading.
Email uses different protocols for pushing mail out versus pulling mail in. The question is specifically about reading mail from the server.
Step 2: Recall SMTP's job.
SMTP (Simple Mail Transfer Protocol) is for sending mail, so it is not the reading protocol.
Step 3: Rule out DNS.
DNS only resolves domain names to IP addresses; it does not fetch messages.
Step 4: Rule out ICMP.
ICMP is a diagnostic protocol used by tools like ping, unrelated to mailboxes.
Step 5: Recall IMAP's job.
IMAP (Internet Message Access Protocol) lets a client read mail kept on the server and keep it synced across devices.
Step 6: Conclude.
The protocol a client uses to read mail from the server is IMAP.
\[ \boxed{\text{IMAP}} \]