Submission form behavior

I have 2 questions

Question 1.
So, I want to show a message after the submission of form that- Check your email for activation of account. But, after setting it multiple times the message which is shown is a default one which says ( thank you for registering and click here to login).

I guess there is some bug, or I am doing something wrong. Do let me know how to fix it.

Question 2.
The user on registration to my site recieves a link for activation of account, and the user can also reply to the same mail. But, I don’t want the user to be able to reply back on the same email. Secondly, I also want to change the email address to a custom email (which I already have for my website), so that activation email looks more legitimate, rather than receiving email from a Gmail account.

Thank You.