What Happens When You Send Email?
You typed in your message and clicked on the
Send button in your mailer. What happens next?
How does email find its way to the final recipient?
Outgoing SMTP Server
Your Internet Service Provider has a special computer
called mail server, which is responsible for
collecting mail from their customers. When you click the
send button, your computer connects to the mail server
and transmits the message along with the list of recipients.
The message is transmitted with Simple Mail Transfer Protocol
(SMTP). SMTP is a language that your mail program uses to
speak to the mail server. SMTP lets your mail program specify
the list of recipients and the text of the message.
The mail server that understands SMTP is frequently called
Outgoing SMTP Server.
Destination SMTP Server
Your destination recipient also has an Internet Service Provider.
They have a mail server too.
When your SMTP server decides that it's time to send your email,
it connects to the destination mail server and transmits the
message to it. They use SMTP to speak to each other. Therefore
the destination mail server is frequently called Destination
Destination SMTP server stores the email message until your
recipient decides to check if some email arrived.
Incoming POP3 Server
When the recipient decides to check the email, his email
program connects to the destination SMTP server and retrieves
mail from the server. This time, they use Post Office Protocol
Version 3 (POP3), which is a language used to receive
mail. Therefore, this server is usually called Incoming
Destination SMTP server for you is Incoming POP3
server for your recipient. When your recipient replies,
the situation reverses - now your mail server becomes a
Destination SMTP server from the viewpoint of the
POP3 service is not necessary. There are other means
to access mail on the destination mail server. For example,
you can use Web browser to access Hotmail® or Yahoo Mail
without downloading all the mail to your computer.
One thing remains unclear. There are millions of SMTP
servers all around the world. How your SMTP server knows
where to send the message?
This information is stored in so called MX records.
MX is not an abbreviation, it doesn't mean anything. The MX
record shows which destination SMTP server must be used for
the specific email address. For example, the MX record for
email@example.com points to the server called slim.aysoft.com.
The database of MX records is maintained by a network called
Domain Name Service (DNS). To get access to the MX records,
you must have access to the DNS server and have a
permission to retrieve MX records.
You can look up MX records for any e-mail address with
special software, such as AY Spy.
As you might have noticed, there are two SMTP servers involved
in sending each message. Your outbound SMTP server is working as a
relay - it accepts your message and relays it to the other
When Internet just started, any SMTP server used to work as
relays - the message used to be passed from server to server
freely. As the email system got abused by spammers, fewer and
fewer servers were working this way. Now all open relays are
closed. The only server that will relay for you is the one
given to you by your Internet Service Provider.
It is also possible to bypass all relays and send email
directly to the destination server.
For more details see our article about