Post Office Protocol (POP) is a protocol an email app uses to retrieve messages from a mail server. The version commonly meant by “POP” is POP3, or Post Office Protocol Version 3, defined in RFC 1939. In its traditional model, POP3 downloads messages to a client and may remove them from the server afterward.
What does Post Office Protocol mean?
Post Office Protocol is the name of a mailbox-access protocol for retrieving email held on a server. The NIST glossary defines POP as a mailbox-access protocol specified by IETF RFC 1939. That RFC specifies POP3, the third version of the protocol.
In practical terms, an email client—such as a desktop mail app—connects to a mail server and retrieves messages from its maildrop. RFC 1939 describes POP3 as a way for a workstation to access a server maildrop dynamically, usually to retrieve mail being held for it.
How does POP3 handle email?
POP3 is primarily for retrieving messages, not for managing a mailbox in depth on the server. Its traditional workflow is to download messages to the email client and then delete them from the server. However, deletion is not inevitable: clients and providers may offer options that change whether downloaded messages remain on the server.
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Because POP3 centers on retrieval, the state and organization of mail can be tied more closely to the client that downloads it. If you use multiple devices, what you see on each can depend on how the email app and provider are configured. Do not assume that every POP3 setup will behave identically.
POP3 vs. IMAP
IMAP is the relevant alternative when you want more extensive mailbox handling on the server. RFC 1939 describes IMAP4 as the more advanced and complex protocol; the key distinction for an email user is that POP3 focuses on retrieving messages, while IMAP supports broader server-side mailbox management.
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| Protocol | Primary role | What that can mean across devices |
|---|---|---|
| POP3 | Retrieves messages from a server maildrop. | Messages may be downloaded to a client and may be removed from the server; device behavior depends on client and provider settings. |
| IMAP | Provides more extensive server-side mailbox handling. | Mailbox handling remains more centered on the server, which can suit access from multiple devices. |
The table describes the protocols’ general roles, not a guarantee about a particular email service. Check your provider’s current setup instructions before choosing or configuring either option.
POP3 ports and connection security
The standards list TCP port 110 for POP3 and TCP port 995 for POP3 over TLS. The IANA service-name and port-number registry records these assignments; RFC 8314 discusses TLS for email access. A registered port does not mean every provider supports it or uses it in the same way, so use the server name, port, and security settings supplied by your email provider.
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Use a TLS-protected connection rather than sending account credentials or message contents without transport protection. The original POP3 standard warns that, without protection, the PASS command sends passwords in cleartext and RETR and TOP send mail in cleartext. Those warnings describe the protocol’s unprotected traffic in RFC 1939, published in 1996; they are not a claim that a correctly configured, TLS-protected connection exposes its contents.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do POP3 servers all support the same features?
No. POP3 has optional commands and extensions, and support varies by server. RFC 2449 defines a capability-announcement mechanism that lets a server report supported extensions and behavior. For setup or troubleshooting, follow your provider’s current documentation rather than assuming a particular optional feature is available.
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