To limit who can send email to your channel, go to the channel name, click More options More options button > Get email address, then click the advanced settings link.

To limit who can send email to your channel, go to the channel name, click More options More options button > Get email address, then click the advanced settings link.

Explanation:
Box 1: No
When group naming policy is configured, the policy will be applied to new Microsoft 365 groups (including teams) created by end users.
For existing Microsoft 365 groups, the policy will not immediately apply at the time of configuration. Once group owner edits the group name for these groups, naming policy will be enforced, even if no changes are made.
Box 2: No
User2 is a member of the Collaboration group, not the Projects group.
You can use attributes that can help you and your users identify which department, office or geographic region for which the group was created. For example, if you define your naming policy as PrefixSuffixNamingRequirement = "GRP [GroupName] [Department]", and User's department
= Engineering, then an enforced group name might be ג€GRP My Group Engineering.
Note: The naming policy is applied to creating or editing groups (including teams) created across workloads (for example, Outlook, Microsoft Teams, SharePoint, Exchange, or Planner), even if no editing changes are made.
Box 3: Yes
User3's department is Projects.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/enterprise-users/groups-naming-policy
https://activedirectoryfaq.com/2021/02/define-teams-naming-policies/

https://docs.microsoft.com/en-us/microsoftteams/meetings-first