2) to check if mydummy's questions and answers are really sent to my
gmail account even if I've subscribed by email from my work email
address
Yes, it was sent to my gmail address :(
However, after logging in google I've found that I can change the
email address that is used for this group:
My settings for this group -> membership and email settings -> use [dropdown list of possible email addresses] for this group with the following settings.
Let's see whether it works or not.