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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-2E253B30-2611-546D-AE5B-1752556FC8E8" xml:lang="en"><title>SMTP
Concepts</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>This section section describes the Simple Mail Transfer Protocol (SMTP)
and its implementation on Symbian platform. </p>
<section id="GUID-DBF1C87D-7360-54B7-8658-B6659BF77F06-GENID-1-10-1-17-1-1-6-1-7-1-4-1-2-2"><title>SMTP protocol</title> <p>SMTP
is the most widely used protocol for sending emails. It is a text-based and <b>push</b> protocol
that cannot <b>pull</b> messages from a remote server on demand. </p> <p>One
or more recipients of a message are specified in a message along with the
message text and other encoded objects. The message is then transferred to
a remote server using a procedure of queries and responses between the client
and server. Either an end-user's email client (Mail User Agent (MUA)) or a
relaying server's Mail Transport Agents (MTA) can act as an SMTP client. The
SMTP client initiates a TCP connection to SMTP server on port 25 (unless overridden
by configuration). </p> <p>SMTP is more suitable for a machine permanently
connected to the Internet. To retrieve messages only on demand, which is the
most common requirement on a single-user computer, a mail client must use
POP3 or IMAP4. POP3 is mostly preferred when single-user computers connected
to the Internet only intermittently. </p> </section>
<section><title>Symbian platform implementation of SMTP</title> <p>SMTP is
a Mail Transfer Agent (MTA) used to transfer emails to a SMTP server which
then forwards them on to a specified destination. </p> <p>Sending an email
generally consists of three phases: connect and authorise to server, send
emails and quit. </p> <p>The SMTP component is responsible for sending email
messages composed and stored in the Message Server’s Message Store. </p> <ol id="GUID-8FCD7F76-46FD-58E9-9EBA-B178B98F0782">
<li id="GUID-A8B5A1FA-DE84-51E8-B2B3-B4FCD073E0D2"><p>The SMTP client initiates
a connection with the SMTP server. Depending on the user’s email settings,
this may have been initiated over a secure SSL/TLS socket on port 465. </p> </li>
<li id="GUID-F18E9E52-DF7A-5127-B6DD-FB08663025E0"><p>Depending on how the
user has configured the email settings and the capabilities of the SMTP server,
SMTP authentication may also be required. </p> </li>
<li id="GUID-74561ABB-4B7A-58E7-B79D-5473C3149476"><p>Mail <b>From</b> and
recipient <b>To</b> are sent. </p> </li>
<li id="GUID-7ABADE92-CAF1-524A-A8AB-288E9849BED1"><p>The message header fields
for the email message stored in the Message Store are then transmitted, each
one separated by a CRLF. </p> </li>
<li id="GUID-7932B3D6-270F-5983-8521-8AC83C7AA450"><p>The last CRLF is sent
to indicate the end of the RFC 2822 header. </p> </li>
<li id="GUID-2A05FF85-4E42-5EEE-A2C5-4763C887E3D2"><p>The message body and
encoded attachments are sent. </p> <p>The encoding format (uuencode or MIME,
character sets) depends on the user’s email settings and locale. </p> </li>
<li id="GUID-7040A4EB-AA7C-5932-B7FF-89595D9256D0"><p>Finally, the body is
terminated by a CRLF. </p> <p>CRLF sequence, and the email is queued by the
SMTP server for sending. </p> </li>
</ol> </section>
<section><title>SMTP example</title> <p>For more details on implementing the
IMAP4 MTM functions, see <xref href="GUID-D73AD200-BE4D-50BF-BCF9-14627DE530B7.dita">example
code</xref>. </p> </section>
</conbody><related-links>
<link href="GUID-4F703F85-080F-5B77-B94D-5449764828F3.dita"><linktext>SMTP MTM</linktext>
</link>
</related-links></concept>