"There are problems with the signature" error occurs for digital signature message if attachment filtering is enabled in Exchange Server 2019 and 2016

Symptoms

In Microsoft Exchange Server 2019 or Exchange Server 2016, assume that you enable attachment filtering on Edge Transport servers to help prevent files in email messages from entering your organization. When you receive an external email with attachments and a digital signature, you could see the following error message:

"There are problems with the signature. Click the signature button for details."

Cause

This issue occurs because the attachment filtering does not process the email correctly. 

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

Resolution

To fix this issue, install one of the following updates:For Exchange Server 2019, install the Cumulative Update 1 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.

For Exchange Server 2016, install the Cumulative Update 12 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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