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Solved: How MIME tag works in Email filter?

The article describes how the MIME tag works for email traffic.


Config snip on FortiGate:

# config emailfilter profile
edit "default"
config imap
set action tag
set tag-msg "SpamByFGT:IMAP"
config pop3
set action tag
set tag-msg "SpamByFGT:POP3"

Below is an example of an email header tagged as spam over IMAP protocol.

Date: Mon, 19 Sep 2022 22:23:33 -0700
Subject: Proxy mode inspection issue
From: User2 <[email protected]>
To: [email protected]
Message-ID: <[email protected]>
MIME-Version: 1.0
Content-Type: text/html; charset=utf-8
SpamByFGT: =?utf-8?Q?IMAP?=
<p style="margin-block: 0px;">Proxy is not working</p>

Tag to MIME header does not modify the email contents[Subject/Body] directly for a user, rather the email client[Outlook/Thunderbird/etc] can take action based on this inserted Header/Attribute.

Alex Lim is a certified IT Technical Support Architect with over 15 years of experience in designing, implementing, and troubleshooting complex IT systems and networks. He has worked for leading IT companies, such as Microsoft, IBM, and Cisco, providing technical support and solutions to clients across various industries and sectors. Alex has a bachelor’s degree in computer science from the National University of Singapore and a master’s degree in information security from the Massachusetts Institute of Technology. He is also the author of several best-selling books on IT technical support, such as The IT Technical Support Handbook and Troubleshooting IT Systems and Networks. Alex lives in Bandar, Johore, Malaysia with his wife and two chilrdren. You can reach him at [email protected] or follow him on Website | Twitter | Facebook

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