How to check DNS records of a domain
Checking DNS records using the command line
The most efficient way to check DNS records of the domain is to use a terminal with the command nslookup. This command will run on almost all operating systems (Windows, Linux, and macOS). The command nslookup shows all DNS records of the domain and below will be provided various nslookup command for the different DNS record types to check using the command line.
Reference:
https://www.hostens.com/knowledgebase/how-to-check-dns-records-of-a-domain/

An outbound port rule can be used to prevent an app from accessing external SMTP servers, but creating a more specific rule that targets the app itself is the most secure and recommended method. By creating an outbound rule to block SMTP ports (like TCP port 25) for the specific application, you can prevent it from sending email while still allowing other outbound connections.
Alternatively, the most secure approach is to create an application-specific rule that blocks the app from connecting to specific remote ports, like 25, or block all outbound traffic by default and only allow necessary connections through application-specific rules.
Reference:
https://learn.microsoft.com/en-us/windows/security/operating-system-security/network-security/windows-firewall/rules

Migrate the users to the new forest using tools like the Active Directory Migration Tool (ADMT). A user can use their existing password in the new forest by either creating a trust that allows authentication from the old domain or by migrating user accounts to the new forest and using the original credentials.
Note:
Migrate users using ADMT
This method moves user accounts to the new forest. The users will be able to use their existing password as long as the password hash is migrated correctly.
1. Set up ADMT: Install the Active Directory Migration Tool (ADMT) on a server in the new forest.
2. Migrate users: Use the tool to migrate users, and ensure that the "Do not rename accounts" and "Do not change password" options are selected in the wizard.
3. Match the SID: To allow for seamless access to resources, you can match the SID (Security Identifier) of the new user account to the original SID by using a tool like the one found in Microsoft's documentation.
4. Reconfigure devices: Update user devices to join the new domain and allow them to access the resources in the new forest.
5. Decommission old resources: Once you are confident in the migration, you can decommission the old forest and its domain controllers.
Reference:
https://learn.microsoft.com/en-us/answers/questions/4374819/how-do-i-migrate-users-from-one-forest-to-another