If you have two different emails setup in outlook, you will have two different pst files, one for each email account. When an email comes it you can divert them to which PST file the email should go to. Sometime they can be configured wrong and both your email account will go to the same PST file although they are different emails address.
I have highlighted the three rec circles around area which point to the data files. The data files in Microsoft Outlook have .pst exention. the default is outlook.pst. Or it can be archive.pst etc etc.
The first red circles will take you to all data files that are in the default folder. They do not give you distinction which is connected to which.
The second circle is around one of the email that you can select and then click on the third red circle (change folder), it will show you what is the current default pst file and where you want to change it. This could be very useful.
Migrating PST file from one PC to the other
You can easily migrate PST file from one PC to the other. Just copy the the pst file to the new folder. Make sue you quit outlook otherwise, it may not copy. When save to the detination folder, click on File>Open Outlook data file … and select this file. It will show all the emails it has.
Migrate email and also setup the old email on the new PC
Copy the data file as above to the new PC and put it in default destination. Create a new email setup just like you would. When everything is complete, use the above image to check every single email account and which PST they are sending data too. It is possible, you default PST will be changed for the new account, it will be set to the default email on the new PC. That can be easily changed using the steps above.