Symptoms

When an .xlsx attachment that's created by Export-Excel is sent through the Edge Transport server that has Attachment Filtering agent enabled in Microsoft Exchange Server 2019 or Exchange Server 2016, the attachment is treated as bad zip file.

Cause

When parsing the data descriptor record of the attachment, the attachment is treated as bad zip file. Currently, when parsing data descriptor record, the signature (0x08074b50) is checked only when compressed size in local file header (LFH) is 0. However, for an .xlsx attachment generated through Export-Excel, compressed size is present in LFH, and still it has data descriptor record with the signature. In this case, the parsing fails, and the attachment is treated as bad zip file.

Resolution

To fix this issue, install one of the following updates:

For Exchange Server 2019, install the Cumulative Update 9 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.

For Exchange Server 2016, install the Cumulative Update 20 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.

References

Learn about the terminology that Microsoft uses to describe software updates.

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