Issue

A user receives an email with some PDF files attached. Attachments are not accessible in MS Outlook 2010. Instead, following message is displayed:

Outlook blocked access to the following potentially unsafe attachments: Important! Invoice 721.pdf, Important! Invoice 721.pdf.

Workaround

This MS Outlook behaviour is a bug introduced by 13 June 2017 Outlook Security Update, and affects all recent versions of MS Outlook (2007 – 2016). In this particular case the bug was triggered by attachments having an exclamation mark in their file names and the offending update was KB3203467.

I don’t believe there is an easy way to open such blocked attachments from within Outlook. I expect Microsoft to provide a proper fix via another update some time soon. In a mean time here a few workarounds that come to mind:

• Ask the original sender to remove exclamation marks from file names and resend the email.
• Open email from a webmail or another email client.
• Remove the offending update. Not recommended as the update fixes some remote code execution vulnerability.

June 2017
Outlook 2010
Windows 7 Pro