Problem: when a new user registers at my site the verification e-mail is not sent (or at least it does not reach the user). I have tried setting up a few test accounts and the notifiction does not get here. Have tried to enter the user name and request password at the login screen as well.

The strange part: it worked fine earlier (until yesterday) - and it still works for users registered earlier! Eg if I type in my own user name and request the password an e-mail arrives shortly...

Anyone who has a clue about what could be wrong? I have looked at the user registration from inside (admin of user accounts) and the e-mail looks correct there...

Another problem as many have mentioned here is that it is impossible to delete users. No error message, the users just don´t get deleted. There are several threads here asking the same question but no answers to that bug (?).

please note, that the "FROM" address is specified in the mail and - depending on the module - might be any user's email address, registered on the portal, i.e. there is no matching. the mail server shall accept any mail from the web server's IP and block anything from outside your network to avoid spam. I agree though, that it would be preferable to be able to specify the FROM address in portal settings and use user's email as REPLYTO only. You might enter this feature request in the public issue tracker (2nd from top) at support.dotnetnuke.com.