Hi Anwar,
As you said it differs from environment to environment and there is some sort of similarlity when you go for Azure Hybrid or SSO deployment, I have come across various environments and issues some of them are :
- Legacy Applications integration
- Onpremise ADFS
- Legacy Operating System for Applications
- Multiple Forests and Domains - all having different FL/DL, User naming standards
- Windows Hello for Business - had issues with multiple domains and single AAD Connect
- Virtual Machine migrations sometimes doesnt work due to the configuration on the source servers customization
- Compliance and Security policies tagging in O365 is very good but testing is required prior to deployment wider audience
- Conditional Access Policies is a excellent tool but requires lot of testing and mapping of user base and devices
- If you are starting try implementing Zero Trust so security is important and baselining the current env will be good
- Password Policies and implementaton - read about it over here in the faqs - active-directory-faq
- Follow the checklist and all the important bits - active-directory-deployment-checklist-p2
Hope this helps and provide some info for your project.
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