It seems at present it is not possible to send mail from RouterOS to an SMTP server that requires authentication or that is accessible only by domain name i.e. IP address changes. I would think that soon, all SMTP servers will be this way.
Fortunately, I have one server that does not require authentication. It is provided by my upstream ISP and I have to be on their network to use it. So, it is authenticated but not with the normal method of sending user name and password.
I imagine that authentication would be simple to add so I do hope it is included in the next version. Then, I would be able to use multiple SMTP servers in case one was down.
All of our mail servers require authentication, but we can send email from the MT routers without authentication if we send the email from an email address with the same domain as the email address it is going to. I do not know if this is a setting on our mail server, but it works.
I have an alias that I send the Router messages to and then it sends it to what ever domain or other address I want.
Send your e-mail directly to the SMTP server, that your mailbox resides on. This SMTP server *MUST* accept this mail then - you don't expect sender of e-mail directed to you to authenticate, right?
Authentication is only needed when you relay through some SMTP server.