thieving outlook

I have a supposedly new problem told to me by both Microsoft tech support  and Apple tech support. I have Office for Mac 2011 and am running Maverick as an os. I have gmail as my default email client and am using mac mail as my mail reader. Outlook that  is bundled in with word,excel and powerpoint, is the problem. I do not use outlook and usually have it disabled, but on occasion I get an email that requires me to open it, when I do, all the mail in my gmail and mac mail is transferred into outlook and deleted from gmail and mac mail. I have had issues with mail disappearing in outlook before so I do not want to use it on a permanent basis, I would prefer to have it available but not as a default email client. I am looking for a way to use it without causing it to transfer and then delete mail from my other mail accounts. Any Ideas Please?