Can't gain access to my database created though Visual Studio?

When you create a database on the server (using SQL Server Management Studio), you don't have to (and should not!) fiddle around with the database file(s) anymore - let the server handle that for you.

Instead: do a Add Connection in Visual Studio and then specify the server instance (DEV-5\SQLEXPRESS) and the database name (emailDatabase) in your connection dialog.

With this, you're connecting and using a SQL Server database the way it's intended to be used - on the SQL Server instance itself. This is much easier, and much less hassle, than having to struggle with "free-floating" .mdf files and attaching them to your solutions and stuff like that....

So here - fill in DEV-5\SQLEXPRESS into your "Server name" dropdown, and then use the "Select or enter database name" option and enter your database name (or pick it from the dropdown) - it should be there!

DO NOT use the "Attach a database file" option - this is the free-floating .mdf "feature" which is rather clumsy and hard to use and error-prone - again: I recommend not using that...