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<blockquote type="cite"
cite="mid:5952d95c-28f9-4e62-8a05-cfdf32fe32f4@tait.net.nz">What
I've found is that the problem is triggered by having a multi-part
message, where one or more parts contains multiple
Content-Transfer-Encoding headers...
</blockquote>
<p>This behaviour comes from [1,2,3]:<br>
</p>
<p>
<blockquote type="cite">Messages with ambiguous content should be
treated as a security risk. In particular, if MIME::Parser is
used in an email security tool, ambiguous messages should not be
delivered to end-users.</blockquote>
</p>
<p>Per default, Amavis delivers them, but flags them as
"CC_UNCHECKED,3", which is a dedicated subcategory for this case.<br>
</p>
<p>[1] <a class="moz-txt-link-freetext" href="https://gitlab.com/amavis/amavis/-/issues/112">https://gitlab.com/amavis/amavis/-/issues/112</a><br>
[2] <a class="moz-txt-link-freetext" href="https://metacpan.org/pod/MIME::Entity#ambiguous_content">https://metacpan.org/pod/MIME::Entity#ambiguous_content</a><br>
[3] <a class="moz-txt-link-freetext" href="https://metacpan.org/pod/MIME::Parser#ambiguous_content">https://metacpan.org/pod/MIME::Parser#ambiguous_content</a><br>
</p>
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