Understanding the protocols for sending and receiving emails.
Electronic mail (email) relies on a set of application-layer protocols to function. The primary protocol for sending email is the Simple Mail Transfer Protocol (SMTP). When you send an email from your email client (like Outlook or Gmail's web interface), the client communicates with your outgoing mail server using SMTP. SMTP is a 'push' protocol; it is used to push messages from a client to a server, and from that server to the recipient's mail server. It operates on the well-known port 25 (or 587 for secure submission). Once the email arrives at the recipient's mail server, it sits in their mailbox waiting to be retrieved. This is where retrieval protocols come in. There are two main ones: Post Office Protocol 3 (POP3) and Internet Message Access Protocol (IMAP). POP3 is a very simple protocol. When an email client connects using POP3 (on port 110), it typically downloads all new messages from the server to the local device and then deletes them from the server. This 'download-and-delete' model means emails are tied to a single device. IMAP (on port 143) is more modern and flexible. It allows the client to view and manage emails directly on the server. The emails remain on the server, and the client just synchronizes a local copy. This means you can access all your emails from multiple devices (phone, laptop, etc.) and any changes you make (like deleting a message or moving it to a folder) are reflected everywhere. Because of this, IMAP is the more common protocol used today.