>>Thanks, Sergey. I think, something got misconfigured when I choose Opera to be my default mail client. I then changed it back to Outlook and instructed Opera to use Outlook as a mail client, but perhaps it was not enough. I am just wondering where should I look and how can I fix the problem, because it would be convenient to just press a button while reading topic in Help.
>
>I don't use Opera so cannot be of any help.

I think, Opera is irrelevant here. I am currently looking through the registry for maito keyword. I found this
"C:\PROGRA~1\MICROS~2\Office\OUTLOOK.EXE" -c IPM.Note /m "%1" and wondering if somebody with Outlook can verify, if it's correct.

And I found also
rundll32.exe "%ProgramFiles%\INTERN~1\hmmapi.dll",MailToProtocolHandler %1