1.Check for ECP i.e weather the system accepts all the numbers or alphabets or spl charteristics.here we had derived 3 Equalence classes.
2.check for Boundary value analysis i.e if the req says the login id must be 8 chars long (excluding domain name,ex:xxxxxxxx.gmail.com)then check the loginid for 7 chars and 9 chrars.
3.Check weather the loginid accepts the user name starting with caps letter or number or spl charaters.
4.the spl characters used generally are '_',"." aprt from this the system automatically gives u the '@"symbol.
5.check weather the system accepts
a.more than one spl symbol..i.e firstname.lastname@example.orgemail@example.com@gmail.com
b.The same spl characters for more than once i.e firstname.lastname@example.org
6.Check for comination of equelnce classes.
i.e combining alphabets and numbers..i.e email@example.com
7.check the mail can be of same domain name i.e firstname.lastname@example.org
8..apart from this u can even test the GUI of the login field,when we move the curser on to text field the arrow pointer of mouse must become "I" shape(part of cursery testing), the curser must be blinking in the testfield so as to make the user to pay attention,and even in some aplications the textfield where the cursor blinks will be in highlighted.