I have designed a book wrapper in CMYK mode in Photoshop cs5. I am using laptop for designing. When I send the design through mail the colours are getting changed. What should be done to get the same output
Since others have commented about monitor calibration, I'll talk about another issue it might be.
The issue is likely to do with how browsers interpret the CMYK values, since computers display in RGB.
To quickly answer your question, there is nothing you can do to change how a CMYK image will be displayed inside an RGB color space, that I'm aware of anyway.
That being said, if this is for print, stop previewing it inside your browser and open it inside the appropriate application for whichever file format you're using. For example, if I were to send someone a CMYK PDF, it will look as if the colors are inverted inside my email client, but when it's opened outside of a browser (inside Acrobat for example) the colors will be displayed pretty much how they should be.
If this design is not intended for print, then you need to switch the colorspace from CMYK to RGB.