what program or software do i need to open these email attachments..

it opened with notepad

File Description Generic data file created by a specific application and typically accessed only by that application; may contain data in text or binary format; text-based DAT files can be viewed in a text editor.

Many programs create, open, or reference DAT files; some examples include:

Microsoft Visual Studio, Corel WordPerfect, Nero ShowTime, Nullsoft Winamp, SoftVelocity Clarion, Ontrack EasyRecovery, Runtime GetDataBack, and MapInfo software.

Program(s) that open dat files
Windows Original program that created the file
May be viewable with a text editor

Ask the person that sent you the email, as Char_X said, its such a generic extension that we can't give you the answer.

Thanks guys. Your response helped me resolve the issue.