About Email Magnifier email validation: learn about SMTP

SMTP

Simple Mail Transfer Protocol is a standard communication protocol for sending email messages.
Since the early 1980s it is one of the most used protocol types worldwide.
SMTP is used by email software mostly for sending mail, while the POP3 (Post Office Protocol 3) or the IMAP (Internet Message Access Protocol) for receiving mail.
All modern email client programs support SMTP.
The SMTP settings maintained in an email client include the IP address of an SMTP server (along with the addresses of either a POP or IMAP server for receiving emails).

ESMTP

Extended Simple Mail Transfer Protocol completes the original protocol for sending e-mail enabling to sent graphics, audio, and video files, and text in various national languages.

We use these commands when we verify email address

• Connect

  It's not actually a real command, but it is the first action we need to do it to start SMTP communication. There only two possible responses to this.

  Code	Description
  220	<domain> Service ready
  421	<domain> Service not available, closing transmission channel

• HELO

  It is an alternative command to start the conversation, pointing that the server is using the ESMTP protocol. The responses are similar.

  Code	Description
  250	Requested mail action okay, completed
  421	<domain> Service not available, closing transmission channel
  500	Syntax error, command unrecognized
  501	Syntax error in parameters or arguments
  504	Command parameter not implemented
  521	<domain> does not accept mail [rfc1846]

• EHLO

  An alternative command to start the conversation, underlying that the server is using the Extended SMTP protocol.

  Code	Description
  250	Requested mail action okay, completed
  421	<domain> Service not available, closing transmission channel
  500	Syntax error, command unrecognized
  501	Syntax error in parameters or arguments
  504	Command parameter not implemented
  550	Not implemented

• MAIL FROM

  With this SMTP command the operations begin: the sender states the source email address in the “From” field and actually starts the email transfer.

  Code	Description
  250	Requested mail action okay, completed
  421	<domain> Service not available, closing transmission channel
  451	Requested action aborted: local error in processing
  452	Requested action not taken: insufficient system storage
  500	Syntax error, command unrecognized
  501	Syntax error in parameters or arguments
  552	Requested mail action aborted: exceeded storage allocation

• RCPT TO

  It identifies the recipient of the email, if there is more than one recipient, the command is simply repeated address by address.

  Code	Description
  250	Requested mail action okay, completed
  251	User not local; will forward to <forward-path>
  421	<domain> Service not available, closing transmission channel
  450	Requested mail action not taken: mailbox unavailable
  451	Requested action aborted: local error in processing
  452	Requested action not taken: insufficient system storage
  500	Syntax error, command unrecognized
  501	Syntax error in parameters or arguments
  503	Bad sequence of commands
  521	<domain> does not accept mail [rfc1846]
  550	Requested action not taken: mailbox unavailable
  551	User not local; please try <forward-path>
  552	Requested mail action aborted: exceeded storage allocation
  553	Requested action not taken: mailbox name not allowed

• QUIT

  It terminates the SMTP conversation.

  Code	Description
  221	<domain> Service closing transmission channel
  500	Syntax error, command unrecognized