Could you please teach me how I can block abc@def.com's e-mails from my gmail account?
From your gmail screen, click on Settings, which is the third link from the right of the top line. Then click on Filters, which is the fourth link from the left on the top line. Follow the instructions to filter messages. I would recommend not only setting up filters to block undesired messages, but also to forward messages automatically to other accounts, etc.
I am overwhelmed by the number of messages of a google group, but does not want to unsubscribe from it because I find the group important to me. What can I do?
There are many options. For example, you can access the google group site and set your delivery option to one a day.
