IMAP vs POP3
Also known as: IMAP4, POP3, email protocol, port 993, port 995
IMAP and POP3 are the two protocols for retrieving email.
IMAP keeps your email stored on the server, syncing read/unread status and folders across all your devices. POP3 downloads email to one device and typically deletes it from the server: fine for one device, problematic when you check email on multiple devices.
IMAP vs POP3, explained at three levels
At home
When you set up email in an app like Outlook or Thunderbird, you're usually choosing IMAP. IMAP keeps your emails on the server (like Gmail's servers) and shows you the same inbox on your phone and computer. POP3 downloads emails to one device: you might miss them on another.
At work
For business email on multiple devices, IMAP is always preferred. Emails, read status, and folders stay in sync between your laptop, phone, and webmail. POP3 was designed for a world where people had one computer and is rarely used for professional accounts today.
At home
IMAP uses port 993 (with SSL/TLS) or 143 (with STARTTLS). It keeps all email on the server; your client downloads headers for display and full messages only when opened. Folders, read/unread, flags, and drafts sync across all clients. POP3 uses port 995 (SSL) or 110; it downloads all messages and optionally deletes them from the server.
At work
IMAP IDLE allows email clients to receive push notifications of new messages rather than polling: more efficient than having clients check every few minutes. For corporate environments, Exchange ActiveSync (Microsoft's protocol) and modern APIs (Microsoft Graph, Gmail API) increasingly replace raw IMAP/POP3 for better functionality and mobile push support.
At home
IMAP treats the server as the source of truth. Each folder is a server-side mailbox, and each message gets a UID (unique identifier) plus a UIDVALIDITY value, so a client can ask only for messages it hasn't seen. Extensions such as CONDSTORE and QRESYNC let a reconnecting client fetch just the flag changes and deletions since its last sync. In my view, POP3 has no such shared state, which is why it can't keep several devices in step.
At work
In email migration scenarios (moving users between mail servers), IMAP-to-IMAP migration tools (imapsync, Google Workspace Migration Tool) copy all folders and messages while preserving read/unread status and timestamps. IMAP quotas and server-side filtering (Sieve scripts) are server administration concerns. Email archiving solutions often connect to IMAP to capture all messages for compliance retention.
Real-world examples
At home
Aisha set up her personal email in Thunderbird using IMAP. Emails she reads on her phone are already marked as read in Thunderbird, and emails she deletes are gone from both, because they're synchronized through the server.
At work
Marcus's company moved from an old hosted email provider to Microsoft 365. The migration tool used IMAP to read every mailbox from the old server and copy it into Exchange Online, preserving folders and timestamps.
How it compares
| feature | IMAP | POP3 |
|---|---|---|
| Email storage | Stays on server | Downloaded to device |
| Multi-device sync | Yes: all devices see same state | No: one device gets the mail |
| Read/unread sync | Yes | No |
| Folder sync | Yes | No (inbox only) |
| Offline access | Cached locally | Full local copy |
| Recommended for | Multi-device (almost always) | Single device, local archive |
For analysts
Understanding IMAP vs POP3 helps BAs and operations teams advise on email client setup for remote or hybrid workers, and is relevant when analyzing email system migration projects.
History & origin
POP (Post Office Protocol) was created in 1984, POP3 in 1988: designed when people had one computer and email was stored locally. IMAP (Internet Message Access Protocol) was created by Mark Crispin in 1986 as a more sophisticated alternative, keeping messages on the server for multi-device access. As smartphones made multi-device email universal, IMAP became the standard. POP3 remains supported but is rarely recommended for new setups. Both have been largely abstracted away by hosted email services (Gmail, Outlook), but remain relevant for email client configuration.