IMAP vs POP3 email protocols

Both two (IMAP and POP) are application layer Internet protocols to retrieve email. The main difference is the way they treat the server's Inbox.

IMAP: Internet Message Access Protocol

In IMAP, messages are left always on the server. You can think of it as a window to the contents of the mail server. So, the main advantage is that the changes you make to your folders will be available from any location you access your email.

The current version is IMAP4rev1 (1996). The first version appeared in 1986.

• Messages always on server.
• Online and offline mode: allows you to work with the local copy of the old messages.
• Partial fetch of messages (not download the entire message).

Pros:

• Changes made to the folders and messages available from any location.
• Possibility of backing up messages with offline mode.
• Several clients can connect to the mailbox.
• Allows downloading part of the message (text part).
• Allows transfer of messages between different mailboxes (email accounts).
• Server-side search (not need to download the entire mailbox to the local PC).
• Works well with large mailboxes.

Cons:

• More complexity in the server side (for example, for the multiple accesss).
• Uses more bandwith. Particularly when sending a message has to be sent twice: one for the target emails (SMTP protocol), and another for the server sent mailbox to keep a copy of the sent messages.
• Slower access to a new unretrieved email.

POP: Post Office Protocol

Implemented in 1984 (POP1). Current version is POP3.

• Downloads all messages to the local Inbox.
• Messages are usually deleted from server (although you can keep copy).

Pros:

• Simpler to implement in server-side.
• More widely spread protocol: all email servers implements it.

Cons:

• Not possible to work with folders in server side.
• Local changes in folders are not available to other clients.
• Slow with large mailboxes.
• Have to download entire messages.