I replaced the firewall, moved DHCP off the server to the new firewall, and tested that everything was working.I had no issues with network connectivity once that was done.
Installed a Heic extension and signed into Dropbox.
Changed passwords and reset multi-factor methods for the compromised user, as well as revoked all current sessions.
Discovered that the Active Directory to Microsoft Entra ID sync issue was caused by external DNS resolution, ultimately the root of it being incorrect DNS forwarders on all domain controllers from a legacy configuration. We have set external DNS forwarders to use going forward.
Overhauled the customer's server infrastructure to separate domain controllers from the app server as well as improve other security configurations. We have drastically improved security, redundancy, and reliability for the customer's on-premises infrastructure. Additionally, we have moved to the new Entra Cloud Sync instead of the legacy Entra Connect Sync for syncing Active Directory users to Entra ID.
Implemented DKIM and DMARC email security and anti-impersonation technologies to improve deliverability and eliminate the possibility of attackers impersonating the customer's public email domain.
Checked network settings and several other things
The server updates have been manually completed.
The Windows Updates for this server have been manually completed.
The client has not proceeded with the quote in a timely manner.
Enabled ports on the firewall to allow WiFi calling and messages to be received without interruption.
During communication with the client, Susan, it was identified that there is currently a server issue occurring with Yahoo's servers. The client has confirmed they have not experienced any further issues with their account as of today.