Redmine

Hi, Everyone.

I quite new in Redmine but I found it awesome. I quickly manage everything but I'm stuck in configuring Email notifications.

I am encountering this error:
An error occurred while sending mail (504 5.7.4 Unrecognized authentication type )

I know that this is simple issue concerning credentials but I would like to seek out confirmation if I am configuring the right way.

I tried to browse the install location and found this file "properties.ini"

Below it, there is an entry that looks like this:

[SMTP]
smtp_host=<our server email server ip>
smtp_port=25
smtp_user=<my credentials>
smtp_password=<password>
smtp_protocol=none

My questions are:

1. Is this the only entry that I should look at in terms of Redmine?
2. What is the smtp_protocol? I'm not quite familiar with this one.
3. Our credentials are manage by a domain, should I input my smtp_user like this "Domain Name\User Name"?

I hope someone can help me with this.

Thanks a lot a more power!