What ports does email use? SMTP, IMAP & POP3

If you have ever configured an email client or mail server, you have run into a confusing pile of port numbers. Email is not one protocol but three — one for sending and two for receiving — and each comes in a plaintext and an encrypted flavor. This guide explains every email port, what it does, and which ones you should actually use. Every port links to its full ProtocolPorts entry, or you can browse all ports.

Email ports at a glance

Sending mail vs receiving mail

The single most important distinction is between sending and receiving. They use entirely different protocols.

Sending is handled by SMTP (Simple Mail Transfer Protocol). Receiving — pulling mail from a server into your inbox — is handled by either POP3 or IMAP. A full email setup therefore uses one sending port and one receiving port.

Sending: SMTP ports

Port 25 is the original SMTP port, but its role has narrowed. Today it is used almost exclusively for server-to-server relay — one mail server handing a message to another. Most ISPs and cloud providers block outbound port 25 from end users to fight spam, so you should not configure your mail client to send on it.

For a mail client to submit a new message, use a dedicated submission port:

• Port 587 is the modern submission standard. The client connects in plaintext and upgrades to encryption with STARTTLS, then authenticates with a username and password. This is what you should use.
• Port 465 is SMTPS — the TLS handshake happens immediately (implicit TLS) before any SMTP commands. Once deprecated, it was reinstated and is now a perfectly valid, secure choice.
• Port 2525 is a non-standard fallback some providers offer when networks block 587 and 465.

Receiving: POP3 and IMAP ports

POP3 downloads messages and, by default, deletes them from the server — good for a single device, awkward for several. It runs in plaintext on port 110 and over implicit TLS on port 995.

IMAP keeps messages on the server and synchronizes read/unread state and folders across every device you own. It runs in plaintext on port 143 and over implicit TLS on port 993. For modern accounts, IMAP over 993 is the better default.

The cleartext vs TLS pairs

Notice the pattern: nearly every email protocol has a plaintext port and a secure twin.

• SMTP submission 587 (STARTTLS) — SMTPS 465 (implicit TLS)
• POP3 110 — POP3S 995
• IMAP 143 — IMAPS 993

On the plaintext ports, your username, password, and message contents can travel over the wire unencrypted unless STARTTLS successfully upgrades the connection. On a hostile network, anyone in the path can read them. Always prefer the TLS variants, and configure clients to require encryption rather than fall back silently.

Why 587 + TLS is the modern submission standard

Port 25 was never designed with end-user authentication in mind, which made it a favorite for spammers relaying junk mail. The IETF separated message submission (authenticated, from a user) from message relay (between servers) and assigned submission to port 587. Combined with mandatory STARTTLS and SMTP AUTH, this gives you an encrypted, authenticated channel that mail providers can rate-limit and monitor — which is exactly why it is the recommended way for clients to send mail.

Open-relay and credential risks

Two classic email security failures are worth flagging:

• Open relay. A misconfigured SMTP server on port 25 that accepts and forwards mail from anyone becomes a spam cannon and lands on blocklists. Lock relaying to authenticated submission.
• Credential theft. Using plaintext 110, 143, or unencrypted 25 exposes credentials to network sniffing. Enforce TLS everywhere and disable the plaintext ports where you can.

Conclusion

Email uses one port to send and one to receive, each with a secure version you should always prefer: submit on port 587 or port 465, and fetch on port 993 (IMAP) or port 995 (POP3). Leave port 25 to the servers, require TLS, and look up any unfamiliar port on ProtocolPorts.