If you send mail from your company account, but through the smtp server with the personal account's credentials, gmail will automatically switch the sending address so recipients see the message as being sent from the personal address. Tools/Account Settings, select an account in the left pane, then click Edit SMTP Server in the lower right pane. Does the User Name of the smtp match that of the selected account? If not, select a different server in the Outgoing Server (SMTP) drop-down. Multiple account may use the same server, i.e. imap.gmail.com or smtp.gmail.com, but have different User Names and passwords. If it's necessary to create extra smtp servers, select Outgoing Server (SMTP) at the bottom of the left pane of Account Settings.