IMAP stands for Internet Message Access Protocol. It is the standard that lets an email app read and manage messages that stay stored on a mail server, so the same mailbox looks the same on your phone, laptop and web browser. If you searched for the "IMAP full form" or "what is I M A P", that is the answer. This guide explains what IMAP does, how it works, which ports it uses, how it differs from POP3 and SMTP, how to set it up, and how to fix common connection problems.
IMAP full form and meaning
IMAP is short for Internet Message Access Protocol. The word "access" is the key. IMAP does not send mail. It gives a client controlled access to mail that lives on the server: it can list folders, fetch messages, search, mark messages as read, flag them, move them and delete them. All those changes are stored on the server, which is why every device that connects sees the same state.
IMAP was created in the 1980s, and the version most clients use is IMAP4rev1, specified in RFC 3501. A newer revision, IMAP4rev2, was published as RFC 9051 in 2021. Most people never need to know the version, but it explains why you see "IMAP4" in some documents.
How IMAP works
- Connect and log in. The client opens a connection to the IMAP server, normally with TLS, and authenticates with a user name and password or an OAuth token.
- Select a folder. The client chooses a mailbox such as Inbox. The server reports how many messages it contains.
- Fetch what is needed. The client asks for message headers first, so it can show a list quickly, and downloads full messages or attachments only when you open them.
- Change state. When you read, flag, move or delete a message, the client tells the server, which records the change.
- Stay up to date. With the IDLE extension, the client holds a connection open and the server tells it when new mail arrives, so messages appear without constant polling.
The mail itself arrives at the server through SMTP and the receiving mail transfer agent, as explained in our guide to the mail transfer agent. IMAP is the last step, where you read it.
IMAP ports and security
| Port | Security | Notes |
|---|---|---|
| 993 | IMAP over implicit TLS (often labelled SSL/TLS) | Preferred; encrypted from the first byte |
| 143 | IMAP, upgraded with STARTTLS | Starts in plain text and upgrades; make encryption required |
Always use encryption, because the connection carries your password and your messages. If your app offers "None" as a security option, do not use it with real accounts. Our article on email SSL and TLS explains the difference between the two modes.
IMAP vs POP3
| Feature | IMAP | POP3 |
|---|---|---|
| Where mail lives | On the server | Downloaded to one device, often removed from the server |
| Multiple devices | Same view everywhere | Each device may see different mail |
| Folders and flags | Synced | Mostly the inbox only, with no sync of state |
| Storage | Uses server space | Uses device space |
| Offline use | Possible with cached copies | Natural, since mail is local |
For nearly everyone who reads mail on more than one device, IMAP is the better choice. See IMAP vs POP3 vs SMTP compared for the full picture.
IMAP vs SMTP
IMAP and SMTP do opposite jobs. SMTP sends mail from your app to a server and between servers. IMAP lets your app read mail that has already arrived. A normal mail account needs both: an incoming server (IMAP) and an outgoing server (SMTP). Read what SMTP stands for for the sending side.
How to set up an email account with IMAP
- Find the settings. Your mail provider publishes the IMAP server name, port and security setting. A typical set looks like imap.example.com, port 993, SSL/TLS.
- Enter the incoming server. In your email app, add an account manually and choose IMAP as the account type.
- Enter the outgoing server. This is the SMTP server, for example smtp.example.com on port 587 with STARTTLS.
- Use the correct user name. Many providers want the full email address.
- Authenticate properly. Some providers require an app-specific password or OAuth sign-in instead of your normal password. Check their instructions.
- Test. Send a message to yourself and check that the inbox updates.
Common IMAP problems and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| "Authentication failed" | Wrong password, or the provider requires an app password or OAuth | Check provider rules and the full user name |
| Certificate warning | Host name does not match the certificate | Use the exact server name given by the provider |
| Cannot connect | Firewall blocks the port, or wrong security mode | Match 993 with SSL/TLS and 143 with STARTTLS |
| New mail does not appear | Client is not syncing or IDLE is blocked | Refresh the folder list; check sync settings |
| Mailbox full | The server stores everything | Delete or archive old mail |
Some servers also limit simultaneous connections. If you use several apps at once, you may hit that limit.
IMAP for developers
Applications that read email, such as support inbox tools, can use IMAP libraries to connect, search and fetch messages. If you only need to receive mail into an application, a webhook-based inbound service may be simpler than polling an IMAP mailbox. See our guide on inbound email processing.
IMAP is for reading, not sending. If your app needs to send mail, use an SMTP service or API. Our guide to SMTP or API helps you choose.
What IMAP can do that simpler protocols cannot
- Folders and flags. Folders such as Sent, Drafts and Archive live on the server, and flags such as read, answered and flagged are stored with each message.
- Server-side search. The client can ask the server to search by sender, subject, date or text, without downloading the mailbox.
- Partial fetch. A client can download only the headers, or only one attachment, which saves time and data on a mobile connection.
- Push-style updates. The IDLE extension lets the server tell the client when mail arrives.
- Multiple connections. Several clients, for example a phone and a laptop, can use one mailbox at the same time.
Keeping an IMAP account secure
Because an IMAP login exposes the whole mailbox, protect it. Use encryption on every connection, a long unique password or an app password, and two-factor sign-in where your provider offers it. Prefer providers and apps that support OAuth sign-in, which avoids storing your password in the app. Remove old devices and apps from the account when you stop using them. If a client reports repeated failed logins you did not make, change your password and check the account's recent activity.
Moving to a new mail provider with IMAP
IMAP makes migration easier. Because the mail is on a server, a migration tool or a second account in your email app can copy folders from the old server to the new one without downloading and uploading by hand. Copy first, keep the old account for a while, and check that folder structure and message counts match before you switch your domain's MX records. Our guide to migrating email providers covers the sending side of such a move.
Need to send as well as read email? Your mailbox covers reading over IMAP. For sending from your application, we can set up SMTP credentials and authentication for you.
References and further reading
Frequently asked questions
What is the full form of IMAP?
IMAP stands for Internet Message Access Protocol. It lets an email app read and manage messages that stay stored on a mail server.
What is IMAP used for?
It is used to read email on one or more devices while keeping the mail and its state, such as read flags and folders, on the server so every device shows the same mailbox.
Which ports does IMAP use?
Port 993 is used for IMAP over implicit TLS and port 143 for IMAP with a STARTTLS upgrade. Use encryption in both cases.
What is the difference between IMAP and POP3?
IMAP keeps mail on the server and syncs it across devices. POP3 downloads mail to one device and often removes it from the server.
Does IMAP send email?
No. IMAP is for reading mail. Sending uses SMTP, so a normal email account needs both an IMAP or POP3 server for incoming mail and an SMTP server for outgoing mail.