How can i Filter specific part of my mail?

 Regex CheckUnderscore = new Regex(@"(.*?)_(.*?)@ecABC.com");

string checkEmailString = "123_blahlbha@ecABC.com";

string emailClientCode = CheckUnderscore.Match(checkEmailString).Groups[1].Value;
 string emailEncodedCleintCode = CheckUnderscore.Match(checkEmailString).Groups[2].Value;

emailClientCode = 123

emailEncodedCleintCode = blablbha

which is something i want

but if checkEmailString = "blah_blahsopmethingwhahwha,123_blahlbha@ecABC.com,1234_blahlbasha@ecABCerere.com";

the emailclientCode and emailEncodedCleintCode will return wrong values.

all i wanna get is  

emailClientCode = 123

emailEncodedCleintCode = blablbha

thanks very much