Emails not reaching hotmail.

[prale]

I remember at my installation:

When you get to the “postfix screen” select internet site
If your debian setup is correct your domain should already be displayed on the screen. If not, enter the domain without the 'www.' portion (i.e. yourdomain.com)

It recommended me to use mail.yourdomain.com

Can I change this to yourdomain.com again?
Maybe by reinstalling postfix?
Because I think the problem is here.

After this I think I can just use the default settings again:

myhostname = sub.domain.net
mydomain = sub.domain.net.local

And if I use this I can receive the amavis/cron daemon emails again.
But I can't mail to any of my emailboxes, I get a mail returned to sender, so I guess if the first step at installation was without mail. in front, it works fine.