It´s all a matter of what your mailserver allow you to "do".
If you for example have an account running QlikView Distribution Service, that has permissions to send out emails, then you set it to Distribution Service.
If you mail server allow anonmymous senders, then you can set it to Anonymous.
And if the account running QDS do not has rights, then you specify them with Username and password, with Domain\User
There is also difference if you are using a Gmail server that requires SSL or any other mail server that requires SSL.
Below setting just work fine for me. Look at the attached image.
as said by ako All you have to do is confirm from your sysadmins weather it is allowed to send email via anonymous account or there is some specific account you can use there.
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