Change calendar invites default format from Rich Text to HTML on Exchange 2013

I had this question after viewing When clicking on a specific email in Outlook all employees get "Not enough memory or disk space to complete this operation.".

We have many users experiencing the Outlook error "There is not enough memory or disk space to complete the operation", below is an example.

1. User-A creates a calendar appointment on Outlook 2013 64bit (Mailbox on Exchange 2013) and invites User-B, the calendar invite is sent out using Rich text by default.

2. User-B receives the calendar invitation and clicks  "Decline drop-down box and selects EDIT THE RESPONSE BEFORE SENDING", in the response body of the email User=B types "I'm not available that day". User-B check email format by clicking the "Format Text" tab on Outlook 2013 and can see the email will be sent out as Rich text.

3. User-A receives the decline notification email and can read the email with no problems. User-A then clicks Reply or Forward and check which format the email will be sent, again it's selected Rich text by default. User-A types in the body of the email "Can you attend Friday?" and sends the email to User-B.

4. User-B receives the email, but when trying to read or open the email an error pops up "There is not enough memory or disk space to complete the operation" and the content of the email is blanc.

I'm able to replicate this issue with any user on our network. The issue appears to be caused by the Rich text email. Has anyone ever experienced this problem?

Is there a way to change calendar invites default format from Rich Text to HTML on Exchange 2013?

Many Thanks