KoltrixIMAP, POP or Exchange: which protocol should your email client use?
IMAP keeps every device in sync, POP downloads and moves on, Exchange adds calendars and contacts. How to choose, which ports to use and what to avoid.
On this page(9 sections)
- The short answer
- How each protocol works
- IMAP: the mailbox stays on the server
- POP3: download and, often, remove
- Exchange: mail plus everything else
- Sending is separate: SMTP
- The settings you will be asked for
- Passwords, app passwords and OAuth
- Which one for common situations
- Common mistakes
- For administrators
- Key takeaways
When you add an email account to a phone or a desktop app, the setup screen asks a question that most people answer by guessing: IMAP, POP or Exchange?
The choice decides whether your messages stay in step across devices, whether a lost laptop takes your mail with it, and whether calendars and contacts come along. This guide explains each option in plain terms, gives the ports you will be asked for and lists the mistakes that cause most support questions.
The short answer
- Use IMAP for almost every personal or business mailbox where you read mail on more than one device. It keeps everything on the server and shows the same state everywhere.
- Use Exchange (or the provider's own sync) if your organisation runs Microsoft Exchange or Microsoft 365 and you also need shared calendars, contacts and tasks in the same app.
- Use POP only when you have a single device that must keep its own copy and you understand the trade-offs.
If your provider also offers a web app, treat that as the main interface and use clients as extras.
How each protocol works
IMAP: the mailbox stays on the server
With IMAP, your messages and folders live on the mail server. Your phone, laptop and web browser are windows onto the same mailbox.
- Read a message on your phone and it shows as read on your laptop.
- Move a message to a folder and it moves everywhere.
- Delete it once and it is gone from every device.
- Search can run on the server, though many clients also keep a local cache.
The cost is storage and dependence: if the mailbox is full or the server is unreachable, clients fall back to cached mail or show errors.
POP3: download and, often, remove
POP3 was designed for dial-up connections. A client connects, downloads new messages and, by default, deletes them from the server.
- Each device keeps its own separate copy.
- Read marks and folders do not sync.
- If the device is lost and there was no backup, the mail is lost with it.
- Many clients can be set to "leave a copy on the server", which helps but does not sync state.
POP is still useful for archiving mail to a local machine or for a single-purpose device. It is a poor fit for a phone plus a laptop.
Exchange: mail plus everything else
Microsoft Exchange and Microsoft 365 use their own protocols (such as Exchange ActiveSync, Exchange Web Services and the Microsoft Graph API). They sync mail, calendars, contacts, tasks and shared folders in one connection, and they support features such as delegate access, out-of-office and shared mailboxes.
If your company uses Microsoft 365, the Outlook apps connect this way automatically. Other apps often can too, but setup depends on what your administrator allows. If you are planning a move away from Microsoft, see migrating from Microsoft 365.
Sending is separate: SMTP
None of the three protocols above sends mail. Receiving (IMAP, POP or Exchange) and sending (SMTP) are configured separately in a client. For an overview of submission ports and when each is used, see SMTP ports 25, 465, 587 and 2525.
The settings you will be asked for
Your provider's help page has the exact server names. The usual ports are:
| Purpose | Secure option | Alternative |
|---|---|---|
| IMAP (incoming) | 993 with SSL/TLS | 143 with STARTTLS |
| POP3 (incoming) | 995 with SSL/TLS | 110 with STARTTLS |
| SMTP (outgoing) | 587 with STARTTLS | 465 with SSL/TLS |
Choose the encrypted option every time. A plain connection on 143, 110 or 25 can expose your password and messages.
Passwords, app passwords and OAuth
Most mail providers no longer accept your normal account password in third-party clients.
- App passwords: a separate, generated password for one app. Many providers ask you to turn on two-step verification first.
- OAuth sign-in: the client opens a browser window, you sign in to the provider and approve. This is safer because the app never sees your password.
- Basic authentication: a username and password sent as-is. Large providers have been switching it off for IMAP and POP, which is why an old setup suddenly stops working.
If a client that worked yesterday now fails with an authentication error, check whether the provider changed its sign-in rules before you change anything else.
Which one for common situations
| Situation | Best choice |
|---|---|
| Phone and laptop, one mailbox | IMAP |
| Team inbox with shared access | The provider's web app, or IMAP with shared folders if supported |
| Microsoft 365 with calendars and contacts | Exchange |
| One office PC that must keep mail offline | POP, with a backup |
| Archiving old mail to disk | IMAP export or POP download, then back it up |
| Moving from one provider to another | IMAP for the copy, see moving from Google Workspace |
Common mistakes
- Using POP on two devices. Each one steals messages from the other, and folders drift apart.
- Leaving encryption off. Always use SSL/TLS or STARTTLS.
- Setting the wrong SMTP server. Sending then fails or lands in spam. Use your mail provider's submission server with authentication.
- Confusing the web app with a client. Settings in a desktop app do not change how the web app behaves.
- Forgetting the sent folder. In IMAP, make sure the client saves sent mail to the server's Sent folder, so it shows on every device.
- Large mailboxes on small phones. Limit how many days of mail sync to the device.
For administrators
When you set up a custom domain, see which DNS records email needs and how MX records work. When a new teammate joins, give them a short setup sheet with server names, ports and the sign-in method, and a note about which devices are approved. New-hire email setup has a checklist.
Key takeaways
- IMAP keeps devices in sync and is the right default.
- POP downloads and usually removes mail, so each device ends up with its own copy.
- Exchange adds calendars, contacts and delegate features for Microsoft environments.
- Receiving and sending are configured separately; use encrypted ports and OAuth or app passwords.
- If a client suddenly stops working, check for a provider sign-in change first.
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