IMAP vs POP3 (and SMTP): Which Should Your Business Use?

IMAP vs POP3 is a choice between syncing and downloading. IMAP keeps your mail on the server and syncs it across every device, so your phone, laptop and webmail always match. POP3 downloads mail to one device and usually deletes it from the server. SMTP is separate: it sends mail. For business email in 2026, use IMAP for reading and SMTP for sending.

The three protocols in one minute

Every email app needs to do two jobs: receive mail from your mailbox and send mail out. Different protocols do each job.

IMAP (Internet Message Access Protocol) — reads mail that stays on the server. Folders, read/unread status, flags and deletions sync everywhere.
POP3 (Post Office Protocol version 3) — downloads mail from the server to one device. Traditionally the server copy is deleted afterwards.
SMTP (Simple Mail Transfer Protocol) — sends mail, both from your app to your provider and between mail servers across the internet.

So the real question is never "IMAP or SMTP" — you need both. The choice is IMAP or POP3 for receiving, and SMTP for sending either way.

How POP3 and IMAP work

POP3: download to one device

POP3 is one of the oldest email protocols, from an era when people had one computer and a slow dial-up connection. The current version is defined in RFC 1939.

Its model is simple:

The app connects to the server.
It downloads new messages.
It (usually) deletes them from the server.
You read and organise mail locally on that computer.

Many apps offer "leave a copy on the server," but even then POP3 only knows about the inbox. It does not sync folders, sent items, read status or deletions. If you read a message on your phone, your laptop still shows it as new. If you file a message into a folder on your laptop, your phone never finds out.

Where POP3 still makes sense: a single computer, a tiny mailbox quota on the server, or a very deliberate decision to keep mail offline and nowhere else. Those cases are rare in business.

IMAP: sync across every device

IMAP was designed for mail that lives on the server and is accessed from many places. The widely used version is IMAP4rev1 (RFC 3501), and the updated IMAP4rev2 is defined in RFC 9051.

With IMAP:

Your mailbox, including every folder, lives on the server.
Every app — desktop, phone, webmail — shows the same view.
Reading, flagging, moving or deleting a message on one device is reflected on all others.
Apps can keep a local copy for speed and offline reading, but the server is the source of truth.
Server-side features such as filters, spam folders and search work for every device.

That is exactly what a modern business needs: people use two or three devices, colleagues may share mailboxes, and IT needs mail to be backed up centrally, not scattered across laptops.

How SMTP fits in

SMTP sends mail. When you click Send, your app hands the message to your provider's SMTP server (this is called submission), and that server relays it over SMTP to the recipient's mail server. The recipient's server stores it, and their app then fetches it with IMAP (or POP3).

Two practical points:

Your app always needs SMTP settings in addition to IMAP or POP3 settings.
SMTP submission needs authentication (your username and password, or an app password). Unauthenticated sending is how open relays used to be abused by spammers.

IMAP vs POP3 compared

	IMAP	POP3
Where mail lives	On the server	On one device (usually removed from server)
Multiple devices	Fully synced	Each device sees a different picture
Folders	Synced	Inbox only
Read/unread, flags	Synced	Not synced
Sent items	Stored on server, visible everywhere	Stored on the device that sent them
Backup	Central, by the provider	Up to each user's computer
Offline reading	Yes, with local cache	Yes
Server storage use	Higher	Lower
Lost or stolen laptop	Mail is safe on the server	Mail may be lost with the device
Good for business	Yes	Rarely

Ports and encryption settings

Always use encrypted connections. Modern guidance (RFC 8314) prefers implicit TLS — encryption from the first byte — for both reading and sending.

IMAP   993  SSL/TLS (implicit TLS)    recommended
IMAP   143  STARTTLS                  older, upgrade-in-place
POP3   995  SSL/TLS (implicit TLS)
POP3   110  STARTTLS                  older
SMTP   465  SSL/TLS (implicit TLS)    recommended for sending from apps
SMTP   587  STARTTLS                  widely supported for sending from apps
SMTP   25   server-to-server relay    not for sending from your email app

Port 25 is for mail servers talking to each other. Many internet providers and networks block outgoing port 25 from ordinary devices, which is why your email app should use 465 or 587.

Moving from POP3 to IMAP

Many small businesses still run on POP3 because that is what a web host or an old IT setup used years ago. Moving to IMAP is worth it, but there is one trap: with POP3, your old mail may exist only on someone's computer, not on the server. A server-to-server import cannot copy what is no longer on the server.

A safe approach:

Find where the mail actually is. Check each user's email app for local folders and how much mail is stored there.
Import what is on the server first. Use your new provider's import tool to copy whatever the old server still holds. The migration guide explains the options.
Add the new mailbox to the old app as an IMAP account. Keep the old POP3 account in the same app for now.
Drag local folders into the IMAP account. The app uploads them to the server, and from then on they sync everywhere.
Switch MX records to the new provider once mail is in place. MX records explained covers this step.
Remove the old POP3 account from the app once everything is uploaded and checked.

If you are leaving a web host, our guide on migrating cPanel email walks through the whole process.

Choosing the right settings in practice

When you set up an app:

Choose IMAP, not POP3, unless you have a specific reason.
Use your full email address as the username.
Use SSL/TLS on port 993 for IMAP and 465 (SSL/TLS) or 587 (STARTTLS) for SMTP.
If two-factor authentication is on, create an app password for the app.
Let the app auto-detect settings where possible; many providers publish autoconfig and autodiscover records for this.

For app-by-app steps, see connecting email apps, and for choosing between Outlook, Apple Mail and others, see the best email client for business.

How Zomail handles this

Zomail connects email apps over IMAP and SMTP, with CalDAV and CardDAV for calendars and contacts. On Zomail Cloud, IMAP is imap.zomail.io on port 993 (SSL/TLS) and SMTP is smtp.zomail.io on port 465 (SSL/TLS) or 587 (STARTTLS), using your full address and an app password. The built-in importer copies mail from Gmail, Yahoo or any IMAP server in the background without duplicates, and your old mailbox is left untouched. Plans are on the pricing page.

FAQ

Is IMAP or POP3 better for business email?

IMAP. It keeps mail on the server and in sync across every device, supports folders and sent items everywhere, and means a lost laptop does not mean lost mail. POP3 suits only single-device, offline-only use.

Do I need SMTP if I use IMAP?

Yes. IMAP and POP3 only receive mail. SMTP is what sends it. Every email app needs both an incoming (IMAP) and an outgoing (SMTP) server configured.

Which port should I use for IMAP and SMTP?

For IMAP, port 993 with SSL/TLS. For SMTP from an email app, port 465 with SSL/TLS or port 587 with STARTTLS. Port 25 is for server-to-server delivery and is often blocked for normal devices.

Will switching from POP3 to IMAP delete my emails?

Switching itself does not delete anything, but mail that POP3 already downloaded and removed from the server exists only on your computer. Keep the old account in your app, add the new IMAP account, and drag local folders across so they are uploaded to the server.

What is the difference between IMAP and Exchange?

IMAP is an open standard for mail only. Exchange protocols (used by Microsoft 365 and Exchange servers) also sync calendars, contacts and tasks in one connection. Standards-based providers use IMAP for mail plus CalDAV and CardDAV for calendars and contacts.