POP3 (Post Office Protocol 3)

What Is POP3?

POP3 (Post Office Protocol version 3) is an email retrieval protocol that allows email clients to download messages from a mail server to a local device. Once downloaded, messages are typically deleted from the server. POP3 is one of the two main protocols for accessing email (alongside IMAP) and is one of the oldest email standards still in use, dating back to the 1980s. It operates over TCP port 110 (or 995 for encrypted POP3S).

How POP3 Works

When an email client connects via POP3, it authenticates with the server, retrieves a list of new messages, downloads them to the local device, and (by default) deletes them from the server. The entire workflow is one-directional: messages flow from server to client. POP3 doesn't support folder synchronization, server-side search, or message state synchronization across multiple devices. It's a "download and clear" protocol suited to a single-device email experience.

POP3 vs. IMAP

The key difference: POP3 downloads and removes messages from the server; IMAP keeps messages on the server and synchronizes state across devices. For anyone who accesses email on multiple devices — phone, laptop, tablet, webmail — IMAP is almost always the better choice. POP3's main remaining use case is archival: organizations or individuals who want to download all email to a local archive for compliance, storage cost, or offline access reasons. For most modern users and businesses, IMAP has effectively replaced POP3.

POP3 and Email Deliverability

POP3 is a retrieval protocol — it governs how users access their mailboxes, not how messages get delivered to those mailboxes in the first place. Delivery still uses SMTP. The choice between POP3 and IMAP doesn't directly affect deliverability. However, POP3's "download and delete" behavior means messages aren't available for cross-device tracking, which can affect open rate measurement tools that rely on server-side tracking data.

POP3 and Email Verification

Like IMAP, POP3 isn't part of the email verification process. Verification uses SMTP to probe mailbox existence. The existence of POP3 access on a mail server is largely transparent to senders and verifiers. What matters for verification is the SMTP/MX configuration of the receiving domain — whether the domain has valid MX records pointing to active mail servers that confirm mailbox existence.

Security Considerations for POP3

POP3 should always be used with encryption — POP3S over port 995, using TLS/SSL. Plain-text POP3 over port 110 transmits email content and login credentials unencrypted, making them vulnerable to network interception. Most modern email clients default to encrypted connections, but legacy systems or misconfigured clients may still use plain POP3. For organizations running their own mail servers, disabling plain-text POP3 and enforcing TLS is a basic security best practice. Learn about email infrastructure best practices at emailverify.io.