example@abc.com is NOT a username but an email- address (that can be used in the username field to login for Webservices / traveler / ldap / etc. if the server is configured accordingly).
There are different ways to get an email- address for a given username, the easiest might be the usage of the Directory- Class and its method "lookupNames".
Here is an example taken from the Designer Help:
Session session = getSession();
AgentContext agentContext = session.getAgentContext();
Directory dir = session.getDirectory("NameOfYourServer");
String userName=session.getUsername();
DirEntryCollection direc = dir.lookupNames("($Users)",userName,"email");
DirEntry dirent = direc.getFirstEntry()
while (dirent != null) {
String name = dirent.getItemValue("InternetAddress");
System.out.println(InternetAddress);
dirent = direc.getNextEntry(); }
Designer help can be found in many places (locally installed if Designer is installed) or e.g. here