My company uses Office365 and we use Outlook for email communications. I also added my personal email account (I'm using Gmail if it matters) to Outlook. Is there any way to totally disable sending mails from my personal account so I can avoid using personal account to send work emails?
If you really want to block sending out emails from your main account, you can do the following.
In outlook, go to File, then select your gmail account. Now go to Account settings -> Server settings.
Unvold the Outgoing email section and change the server to something like: dontuse.
Hit next to apply the changes. Gmail will attempt to verify and will fail. Not entirely sure if you have to type your password in, but I did do that in my test. Cancel out of the dialog. The changes have been saved regardless.
When you now send an email, the email will be kept in the outbox and not send. In addition, the statusbar will indicate that there was a send/receive error.
Its can be hard to miss, but at least you have a protection against sending emails out.