In the batch of security updates Microsoft released for June 2017, they introduced a major bug which affects Microsoft Outlook 2007, 2010, 2013 and 2016 in a number of different ways.
Run Office Update or Windows Update (depending on the version of Office you are using). The updates released 27 July seem to have resolved these issues.
Email Attachments Blocked
Attachments with two consecutive periods ( “..”or full stops) or an exclamation (“!”) at the end of the filename.
Ask the sender to change the name (remove a period) and resend the email.
Email Attachments Will Not Open if sent as Rich Text
Here the attachment is embedded in the message.
You can also sometimes receive this error
The program used to create this object is Outlook. That program is either not installed on your computer or it is not responding. To edit this object, install Outlook or ensure that any dialog boxes in Outlook are closed.
Ask the sender to change the default send type to HTML in the email options and resend as an HTML email.
It’s best to change this not only per email, but in Outlook’s options for sending mail to HTML.
Outlook Search Does Not Display Full Results / Incomplete
You can try a re-index (available from the Control Panel under Indexing Options)