Key concepts
Email protocols
FortiMail™ Secure Messaging Platform Version 4.0 Patch 1 Install Guide
Revision 2
13
•
Key concepts
This chapter defines basic email and FortiMail concepts and terms.
If you are new to FortiMail units, or new to email systems, this chapter can help you to
quickly understand this document and your FortiMail unit.
This chapter contains the following sections:
•
•
Client-server connections in SMTP
•
The role of DNS in email delivery
•
FortiMail web-based manager modes
•
•
FortiMail high availability modes
Email protocols
There are multiple prevalent standard email protocols.
SMTP
Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending email between:
• two mail transfer agents (MTA)
• a mail user agent (MUA) and an MTA
SMTP communications typically occur on TCP port number 25.
When an email user sends an email, their MUA uses SMTP to send the email to an MTA,
which is often their email server. The MTA then uses SMTP to directly or indirectly deliver
the email to the destination email server that hosts email for the recipient email user.
When an MTA connects to the destination email server, it determines whether the
recipient exists on the destination email server. If the recipient email address is legitimate,
then the MTA delivers the email to the email server, from which email users can then use
a protocol such as POP3 or IMAP to retrieve the email. If the recipient email address does
not exist, the MTA typically sends a separate email message to the sender, notifying them
of delivery failure.
While the basic protocol of SMTP is simple, many SMTP servers support a number of
protocol extensions for features such as authentication, encryption, multipart messages
and attachments, and may be referred to as extended SMTP (ESMTP) servers.
FortiMail units can scan SMTP traffic for spam and viruses, and support several SMTP
extensions. For details, see the Fortinet Knowledge Center article
Supported SMTP-
related RFCs
.
POP3
Post Office Protocol version 3 (POP3) is a standard protocol used by email clients to
retrieve email that has been delivered to and stored on an email server.
POP3 communications typically occur on TCP port number 110.
Note:
For definitions of MTA and MUA, see
Summary of Contents for FortiMail-100
Page 1: ...FortiMail Secure Messaging Platform Version 4 0 Patch 1 Install Guide...
Page 173: ...www fortinet com...
Page 174: ...www fortinet com...
