Block a spammer in your 365 Tenant

 You block a spammer in Defender in a 365 Tenant (as of June 2026, until MS changes their minds and moves it somewhere else)

In defender (security.microsoft.com)

-> Email & collaboration

-> Policies & Rules

->  Threat Policies

-> Tenant Allow/Block Lists

Click on "ADD"

    -> Select Block

In the "Add domains & Addresses" box put in the email address you want to block

Set the duration of the block

Click on "ADD"

User gets a new phone and needs to re-authenticate their Microsoft MFA

Find their user name in ENTRA 

Click on "Authentication Methods"

Click on "Require re-register multifactor authentication"

Have the user try and logon to a MS product.  It will prompt them to scan the QR code to re-register their MFA.

Teams error code 700003

 

Here's what worked for us

Opend a CMD prompt as administrator

Run the command

dsregcmd  /forcerecovery

Log back into Teams