Improvements and fixes
This update fixes the following attachment issues that were reported after the release of the June update. See Outlook known issues in the June 2017 security updates for more information.
When you open an attachment whose file name includes an ellipsis (...) or an exclamation point (!), the files are blocked and you receive a warning message.
If an email message includes an attached email message, and the attached email message's subject line includes an unsafe file name extension (as listed in the Blocked attachments in Outlook Office webpage), the email attachment is blocked for recipients.
You receive an error message when you open attachments in an email message, a contact, or a task that's formatted as Rich Text.