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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.

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