1) No, the email should not use a dynamic from address.
Most hosts will look at the email headers and if the from address is from a different domain, they will consider it to be spam.
Like i have already said, you can clic the From Button in the UE behavior to access the advanced from to settings and use the dynamic binding for the Reply To Address. This way the host sees that the email is coming from a valid allowed address, but when you reply to it, it will goto the person who filled in the form.
2) If you leave the stamp server settings blank, the defaults from the php.ini file will be used. this will only work if the php.ini file is configured with the correct defaults.