Using older versions of Outlook for Mac in business environments
This is a known issue and Microsoft is investigating.
In the meantime I suggest using the default custom attribution
(third option) under **Outlook** menu --> *Preferences...*
--> **Composing**. It contains the name of the person you're
quoting, his email address and the date.
The attribution you've been using includes the subject, which is
redundant since it's already in the subject line of the mail
message, and a list of recipients, which is also redundant because
they're in the To, Cc and Bcc fields.
Hope this helps!