Office 365 E3 Security Defaults

[rincman]

I have office 365 E3 with three users and a fourth that just has a plan 1 mailbox.  I have had this since 2013.  A couple years ago I turned on Modern Authentication.  It did not turn on by default.  At the time, MS Support recommended leaving on all the basic authentication under settings/org settings/modern authentication.  I was reading and see under the identity score in Azure under Security under "Enable policy block legacy authentication" I have a 0 score and it leads me to being able to set security defaults under properties manage security defaults. 

My users use MFA and use the latest version of Outlook desktop, iphone with both built in mail client and outlook mobile, and sometimes the outlook web access.

Before I enable default security I wanted to ask can this cause me to be locked out of the admin and also impact checking email on any devices? 

I looked at the sign-in logs under Azure and do not see protocols listed.  I enabled in the column list protocol type and for all it notes unknown.  Looking here was noted under Modern Authentication before disabling any basic authentication.

Also, what does enabling security defaults this do?  Does it just disable all the basic authentication items under Modern Authentication?  Is it the same as just disabling these manually?

thanks

[#2]

Disabling legacy authentication is one of the things Security defaults cover, see here: https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/concept-fundamentals-security-d...
You can think of it as an equivalent for manually blocking legacy auth, configuring users for MFA and so on. It will not cause you do be locked out of the admin portal, and should not cause any troubles with email clients too, assuming you're using a reasonably recent version.

[#3]

Thanks. When you set the security defaults, does it provide a list of what it will change and can I change anything? Also, I looked at the sign in logs. Is there a way to see if any users are using a legacy authentication. I read I have to look at the app using it and i do not think I have anything using legacy. I just want to confirm.

[#4]

No, you cannot change anything, it's an "all or nothing" deal.