Exchange 2013 CU21 + Edge stripping .xlsx

I confirmed the attachment filter does not have a .xlsx entry added. I disabled all entries, restarted the transport service, and resent the source file. It was still stripped.

I wasn't able to locate a reason in the logs here, or anywhere else:

Edge Server: C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\Edge\ProtocolLog\SmtpSend

Disabling the attachment filter agent allows file to pass, so I was able to get a copy of the affected source file.

I am able to successfully send personal .xlsx files, so to me, it's how this particular .xlsx is being generated.

This FIXES my issue, but I'm on EX2013 CU21

https://support.microsoft.com/en-gb/help/2855809/email-message-attachments-are-removed-incorrectly-on-an-exchange-serve

I extracted a normal .xlsx and compared the [Content_Types].xml

New .xlsx

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>

    <Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">

        <Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/>

        <Default Extension="xml" ContentType="application/xml"/>

        <Override PartName="/xl/workbook.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml"/>

        <Override PartName="/xl/worksheets/sheet1.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml"/>

        <Override PartName="/xl/theme/theme1.xml" ContentType="application/vnd.openxmlformats-officedocument.theme+xml"/>

        <Override PartName="/xl/styles.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.styles+xml"/>

        <Override PartName="/docProps/core.xml" ContentType="application/vnd.openxmlformats-package.core-properties+xml"/>

        <Override PartName="/docProps/app.xml" ContentType="application/vnd.openxmlformats-officedocument.extended-properties+xml"/>

    </Types>

Stripped .xlsx

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>

    <Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">

        <Default ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.printerSettings" Extension="bin"/>

        <Default ContentType="image/png" Extension="png"/>

        <Default ContentType="application/vnd.openxmlformats-package.relationships+xml" Extension="rels"/>

        <Default ContentType="application/xml" Extension="xml"/>

        <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml" PartName="/xl/workbook.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml" PartName="/xl/worksheets/sheet1.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.theme+xml" PartName="/xl/theme/theme1.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.styles+xml" PartName="/xl/styles.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sharedStrings+xml" PartName="/xl/sharedStrings.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.drawing+xml" PartName="/xl/drawings/drawing1.xml" />

        <Override ContentType="application/vnd.openxmlformats-package.core-properties+xml" PartName="/docProps/core.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.extended-properties+xml" PartName="/docProps/app.xml" />

        <Override ContentType="application/vnd.openxmlformats-officedocument.custom-properties+xml" PartName="/docProps/custom.xml" />

    </Types>

What gives?