Sending to the Synology Email ServerThe default configuration is set up to send notification emails to the local server, so if you are using the Synology email server, built into the diskstation, then all that's required is to add your email address to the default ds-admin account in the Contacts tab. The following video shows how.
Sending via your ISPMany ISP's and most companies block emails coming from known broadband addresses to reduce spam, and many ISPs also block outward bound email messages to all addresses apart from their own relay servers for the same reason. It's never a good idea to send emails directly from a standard broadband account - always use the relay server unless you have a business account. Additionally, some ISPs require secure authentication to be able to send emails through their relay server.
So, even if you don't use the Synology email server it's a good idea to set it up to send to your ISP's SMTP relay server. Doing it this way means that setting up Synagios is the same as the above video, so, really simple, and the diskstation's mail server can handle all the difficult bits (authentication, relay servers etc.).