Outlook blocked access to the following potentially unsafe attachments...
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.
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.