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How does IMAP work? The short answer
How does IMAP work? IMAP (Internet Message Access Protocol) keeps your email on the mail server and syncs it to every device you read it on. When you open a message, mark it read, or move it to a folder, IMAP records that action on the server — so your phone, laptop, and webmail always show the same mailbox. Unlike POP3, which downloads mail to one device, IMAP is built for reading the same inbox everywhere.
This is the receiving half of email. In our SMTP guide we followed a message being sent; IMAP is how it gets read. SMTP pushes mail out; IMAP pulls it down and keeps it in sync. Two protocols, one app. Learn how does IMAP work.
What is IMAP?
IMAP is a sync protocol. Your messages live on the server as the single source of truth, and each device holds a synchronized view rather than the only copy. That’s why deleting an email on your laptop also deletes it on your phone — both are looking at the same server-side mailbox.
How IMAP syncs your mail, step by step
- Connect & authenticate to the IMAP server over an encrypted connection.
- Fetch the folder list and headers — subjects and senders load first, so the inbox appears fast.
- Download a message body on demand, only when you open it (which is why large attachments load when tapped).
- Sync your actions back — the app writes read/unread status, flags, folder moves, and deletions to the server.
- Reconcile every device — each client polls or holds an open connection so changes appear everywhere.
the single source of truth
IMAP vs POP3: what’s the difference?
The imap vs pop3 question comes down to sync versus download:
| Dimension | IMAP | POP3 |
|---|---|---|
| Where mail lives | On the server | Downloaded to one device |
| Multiple devices | Synced everywhere | Poor — one device gets the mail |
| Folders & flags | Synced server-side | Local only |
| Offline access | Cached copies | Full local copies |
| Server storage | Uses your quota | Frees the server (often deletes) |
| Best for | Almost everyone in 2026 | Single-device or archival use |
IMAP ports
| Port | Use | Verdict |
|---|---|---|
| 993 | IMAP over implicit SSL/TLS | Recommended — encrypted by default |
| 143 | IMAP with STARTTLS (or plain) | Use only with STARTTLS; avoid unencrypted |
If your mail is missing on one device but present on another, you’re almost certainly mixing POP3 (which grabbed and removed it) with IMAP. Standardize on IMAP and the mailbox stays consistent everywhere.
When to use IMAP vs POP3
- Use IMAP if you read mail on more than one device — which is nearly everyone.
- Consider POP3 only for a single-device setup or to pull a local archive off the server.
Sending is the other half
IMAP gets mail read; SMTP gets it delivered. EmailSendX handles the sending side — authentication, routing, and deliverability — so the messages you send actually reach the inbox your recipients open over IMAP.
Frequently asked questions
Is IMAP used to send email?
No. IMAP only retrieves and syncs mail you’ve received. SMTP handles sending.
Should I use IMAP or POP3?
IMAP for almost everyone — it keeps every device in sync. POP3 only suits single-device or archival use.
Which IMAP port is secure?
Port 993 uses implicit SSL/TLS and is the safe default. Use port 143 only with STARTTLS.
Does IMAP store email on my device or the server?
On the server. Your devices keep synced, cached copies, but the server holds the master mailbox.
Ready to try it?
