can any one explain me how to use the code stage and i want use code for email validation by using C# code

[kirankumarReddy]

How to write the C# code in blueprism and any Dll we want to import for writing C# code

[Denis__Dennehy]

There is a product data sheet availalbe in this portal called: Blue Prism Data Sheet - Extending Automations using the .NET Framework  - that should be your starting point.   My recommendation would be to use a true development IDE if you are doing anything more than a few lines of code.  Then transfer your code into Blue Prism code stages when you are happy with it.   I presume that the SMTP/POP and MapieX email interfaces that are provided by Blue Prism do not do what you need?