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