Fortinet FortiMail-100, Install Manual

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Client-server connections in SMTP Key concepts
FortiMail™ Secure Messaging Platform Version 4.0 Patch 1 Install Guide
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Unlike IMAP, after a POP3 client downloads an email to the email user’s computer, a copy
of the email usually does
not remain on the email server’s hard disk. The advantage of
this is that it frees hard disk space on the server. The disadvantage of this is that
downloaded email usually resides on only one personal computer. Unless all of their
POP3 clients are always configured to leave copies of email on the server, email users
who use multiple computers to view email, such as both a desktop and laptop, will not be
able to view from one computer any of the email previously downloaded to another
computer.
FortiMail units do not scan POP3 traffic for spam and viruses, but may use POP3 when
operating in server mode, when an email user retrieves their email. For more information
on server mode, see
“FortiMail operation modes” on page 19 .
IMAP
Internet Message Access Protocol (IMAP) is a standard protocol used by email clients to
retrieve email that has been delivered to and stored on an email server.
IMAP communications typically occur on TCP port number 143.
Unless configured for offline availability, IMAP clients typically initially download only the
message header. They download the message body and attachments only when the email
user selects to read the email.
Unlike POP3, when an IMAP client downloads an email to the email user’s computer, a
copy of the email remains on the email server’s hard disk. The advantage of this is that it
enables email users to view email from more than one computer. This is especially useful
in situations where more than one person may need to view an inbox, such where all
members of a department monitor a collective inbox. The disadvantage of this is that,
unless email users delete email, IMAP may more rapidly consume the server’s hard disk
space.
FortiMail units do not scan IMAP traffic for spam and viruses, but may use IMAP when
operating in server mode, when an email user retrieves their email. For more information
on server mode, see
“FortiMail operation modes” on page 19 .
HTTP and HTTPS
Secured and non-secured HyperText Transfer Protocols (HTTP/HTTPS), while not strictly
for the transport of email, are often used by webmail applications to view email that is
stored remotely.
HTTP communications typically occur on TCP port number 80; HTTPS communications
typically occur on TCP port number 443.
FortiMail units do not scan HTTP or HTTPS traffic for spam or viruses, but use them to
display quarantines and, if the FortiMail unit is operating in server mode, FortiMail
webmail. For more information on server mode, see
“FortiMail operation modes” on
page 19 .
Client-server connections in SMTP
Client-server connections and connection directionality in SMTP differ from how you may
be familiar with them in other protocols.
For example, in the SMTP protocol, an SMTP client connects to an SMTP server. This
seems consistent with the traditional client-server model of communications. However,
due to the notion of relay in SMTP, the SMTP client may be either:
• an email application on a user’s personal computer