Delivery versus access
SMTP gets a message into the receiving system. IMAP lets a user or app access that stored message later. The two jobs are related, but they happen at different points in the mail flow.
Folders and flags
IMAP exposes folders such as Inbox, Sent, Archive, and Trash. It also tracks message flags, including seen, answered, flagged, deleted, and draft state.
Why IMAP is common
Because messages remain on the server, multiple devices can show the same mailbox view. This makes IMAP a natural fit for modern mail clients, shared access, and server-side filtering.
Examples
Reading mail on several devices
A user reads a message on their phone. The mail app marks it as seen via IMAP, and the desktop client later shows the same message as already read because the state lives on the server.
Server-side folders
When a rule moves a message into Archive or a project folder, IMAP clients can subscribe to that folder and display the same organised mailbox view.
Common issues
- Assuming IMAP delivers mail. IMAP reads stored mail; SMTP delivers it.
- Large mailboxes becoming slow when clients repeatedly resynchronise everything.
- Folder naming differences between clients, especially around Sent, Archive, Junk, and Trash.
- Confusing deleted flags with permanent removal; many IMAP workflows require an expunge step.