Dear Jurgen,
It is a little complicated, and I am also thankful to you for bringing this matter up.
I used to learn SAP as an individual few years ago and had a Consolut-IDES profile at xyz@googlemail.com
Then, fortunately I got a job in a consulting firm and they gave me an S user ID and created a profile with that one, finally I was fortunate enough to pass the certification and thus received my OWN S-user ID with the same email address but with @gmail.com rather than @googlemail.com.
Since the deletion of my post yesterday, I have started using my LinkedIn profile as a reference to sign in as that will remain the same. 
Lastly, I am pleased to talk to you, as like many others I also refer to you as father of MM in my SAP circles and am also a fan of your commitment and knowledge. keep up the great work.