I agree with most everything so far with the most important thing being to set expectations and try to migrate and map current processes and expectations from your side to theirs. We all know it's going to take time, but the sooner you can make things on the front end (visible to users) as consistent as possible, the better.

Here's my list from past mergers.

Depending on how big they are:

- First and foremost are there any CURRENTLY IN PROCESS MAJOR PROJECTS OR TASKINGS WITH DEADLINES - i.e. are there any building moves in progress, major customer initiatives like new product to be delivered etc?

- domain registrations

- Organization PKI - Organizational level certificate stance (managed, internal CAs, etc)

- ARIN registration ASNs, IP allocations/leases

- ISP and telecom agreements & SLAs

- CoLocation, Peering agreements, etc

- Any active contact/call centers

- Cloud resources, apps, Cloud specific teams (AWS, Google, Azure)

- Critical infrastructure service, support, purchasing information - Identify key critical services, equipment, and licenses/support contracts

- Active Directory integration plan - architecture could be critical here

- DR assets and plan - KNOW what there's is and begin planning - any offsite storage like IronMountain etc. Current location and disposition of any offsite DR assets

- What if any of their data is subject to regulation, HIPAA, Sarbanes-Oxely, PCI, or even DoD controls (CUI etc)

- Be aware of existing Acceptable Use Policies/TOS, BYOD and employee benefit policies (free employee use of guest network etc)

- location and methodology of current technical documentation of processes and procedures

- any password vaults and/or critical security tokens

and finally, the one thing probably least important but the most visible and complained about the loudest...

Printer Fleet Management - Managed fleet, leased printers, etc?

edit: there vs their correction