RFC 821, Simple Mail Transfer Protocol
These days, people use email everyday, and me too.
SMTP used in the email.
We can get email list and content by http call.
Because nowadays email service support that.
When you call email list, mail service search their mail box and response with the results.
But in the core of mailing service, SMTP has been inevitable.
Each mailing service communicate with SMTP. POP or IMAP just sugaring these contents.
Then, is SMTP effective protocol? It was.
In the past, only a character, a word, a text are available in the internet.
Today, multi-media exist throughout internet world. Even in your mail.
That means protocol that handle medium should process binary file effectively.
But SMTP can only send ascii 7-bits character.
So when you want to send a video or even ms word file with email, mailing service or client should send after convert binary to ascii code.
It is quietly mess.