SMTP Email
SMTP is the technical term for what most users would consider "outgoing email". It is of course, used for incoming mail as well, but its incoming to the server, not incoming to the user.
SMTP stands for "simple mail transfer protocol", and simple it is. SMTP was updated, extended, or enhanced through the eSMTP protocol, which most people still refer to as SMTP.
So what does it do? SMTP servers can perform several tasks:
- Accept or deny incoming messages from a clients
- Relay messages to another SMTP server
- Deliver a message directly to an email mailbox
That isn't an exhaustive list, but it covers some important tasks.
An important part of many smtp server configurations is the access control. This is mainly due to spam. If a server is not secured properly, it will get bombarded with junk mail and potentially used to send it, too!
SMTP communication can be encrypted using transport layer security (TLS).
The default port for smtp communication is port 25, but many servers also allow authenticated access to port 587 (submission) for outgoing mail. Some ISPs block all outgoing connections on port 25, and some mail server administrators prefer to separate incoming and outgoing services.