There are a few things in Sierra to change from the default install setup.

The reason to change the Spotlight and Safari default settings is because otherwise Sierra sends all that personal info to apple, and who knows where it goes from there.

First go to System Preferences > Spotlight and Uncheck the following:
> Mail & Messages
> Spotlight Suggestions
> Bing Web Searches
> Bookmarks & History

Next, start Safari, open Preferences > Search and Uncheck “Include Spotlight Suggestions”

Then, in Mail, go to Preferences, and for every account you have (except for any accounts ending in me.com or icloud.com) you need to do these steps:

Click the account name in the left hand window, then click the Mailbox Behaviors tab, then Uncheck “Automatically Detect and Maintain Account Settings”. Each time you move to another account, it should ask if you want to save changes.

Still in Mail, click the account in the left hand window, then click the Account Information tab, then go down and click on the Outgoing Mail Server box, from the pop up, choose Edit SMTP server list.

This brings up a new window, again do this for each outgoing mail server: click on the Advanced tab, uncheck the box for “automatically detect and maintain account settings”, saving each time you make the change.