The first 100 days after closing set the course for the rest of the integration. On the technology side the work has four parts: establish what you actually own, stabilise what is risky, decide where each part of the estate should end up, and turn those decisions into a plan with owners and dates.
The common failure is to skip the first part. Teams under pressure to show progress start migrating before they have a reliable inventory, and then find the systems nobody listed halfway through a cut-over. The other expensive failures are quieter: key people leave because nobody told them where they stand, and the synergies in the deal model are never tracked, so nobody can say later whether they were delivered.
When it happens
From closing to roughly the end of the third month. You now have full access and legal control. The target's staff are uncertain about their roles, the business is still settling into new ownership, and any transition services are running against a clock.
Who is involved
- The integration management office, which runs the programme, the cadence and the decision log.
- The IT integration lead and workstream leads for network, identity and email, applications, end-user services and security.
- The security lead, who owns stabilisation and the connectivity gate.
- The target's IT team, who still run the business day to day.
- Finance, for synergy tracking and the cost of integration.
- HR, for retention, organisation design and communications to staff.
- Business owners, who decide what the business needs from each system.
- The seller, if transition services are in place.
The steps
1. Set up the integration management office and its cadence
A small office with clear decision rights keeps a large programme honest. Set the rhythm in the first week and hold to it.
- Workstreams with named leads and scope
- A weekly workstream review and a regular steering group
- One log of risks, actions, issues and decisions
- Decision rights: what a workstream lead may decide, and what goes to steering
- A short, consistent status report to the executive sponsor
2. Establish the baseline
Before changing anything, find out what is there. Diligence gave you the seller's description; now check it against the estate itself.
- Inventory of devices, servers, applications, cloud subscriptions, domains and certificates
- Network topology and addressing, as found rather than as documented
- Contracts and renewals, with notice periods and termination terms
- The IT organisation: who does what, contractors and outsourcers, skills
- A comparison with the diligence findings: what was missing, what has changed
3. Stabilise with security quick wins
Fix the things that could hurt you before integration adds more change. Most of these come straight from the diligence findings and the connectivity gate.
- Multi-factor authentication gaps closed, starting with remote access, email and administrators
- Stale, shared and excess administrator accounts removed
- Critical internet-facing vulnerabilities fixed, and exposed legacy systems retired
- Backups checked with a restore test, with an offline or immutable copy
- Endpoint protection and monitoring extended to everything in the inventory
- The compromise assessment completed if it was deferred to closing
4. Decide the end state for each domain
For each part of the estate, choose one of three broad paths: absorb it into the buyer's platform, keep it separate, or take the best of both, which sometimes means the buyer moves onto the target's system. Decide per domain rather than by default, and write down why.
- Domains to decide: identity, email and collaboration, network, end-user devices, finance, customer systems, HR and payroll, security tooling, service desk
- Criteria: the deal thesis, cost, risk, regulatory constraints, contract dates and business disruption
- Keep-separate cases: regulation, a planned onward sale, or a business that runs better on its own
- One decision record per domain, with its rationale and owner
5. Build the roadmap and track synergies
Turn the decisions into a sequenced roadmap. Dependencies set the order: identity usually comes before email, and the network interconnect before application consolidation.
- Integration waves with dates, dependencies and owners
- Transition services exit dates built in, not added later
- Contract renewal and notice dates that open or close options
- Each synergy with an owner, a baseline, a target, a date and the evidence that will prove it
- Integration costs tracked separately from the savings they are meant to buy
6. Keep key people and their knowledge
The diligence findings will already name the people the business depends on. Work with HR on retention, and start knowledge transfer early rather than when someone resigns.
- Key people confirmed, with retention arrangements agreed through HR
- Honest conversations about roles, as early as the organisation design allows
- Runbooks and documentation written for each critical system
- Shadowing and deputies for single points of knowledge
7. Communicate on a schedule
People fill silence with rumour. Tell staff what will change, what will not, and when they will hear more, even when there is nothing new.
- A regular update to the target's staff on technology changes that affect them
- Advance notice for anything they will notice: new devices, new sign-in, new email address
- A single place to find answers and ask questions
- Customer and supplier messages where integration affects them
Common traps
- Integrating before you have a baseline
- Letting day-one workarounds become permanent
- Moving everything onto the buyer's platforms by default, without checking contracts or the deal thesis
- Synergies in the deal model that nobody owns or measures
- Transition services exit dates that are not in the roadmap
- Losing the one person who knows how the core system works
- Delaying security quick wins until integration is "done"
- Every workstream reporting green while the decision log stays empty
- Loading the target's IT team with integration requests on top of running the business
What you hand over
At around day 100:
- A validated baseline: inventory, topology, contracts and organisation
- A stabilisation report: what was fixed, and the risks that remain
- An end-state decision for each domain, with rationale
- The integration roadmap, with waves, dates and dependencies
- A synergy tracker with owners and evidence
- A key-person and knowledge-transfer plan
- An updated risk register
Network work continues in network integration, and identity and email in identity and email integration.
Where MNA Tools helps
- SubnetSleuth gives you the network part of the baseline: a read-only inventory and topology of the network you inherit, inside the ranges you agreed, exported for the team that runs it next.
- HouseGRC turns the risk register into a ranked, dated remediation plan, tracks supplier consolidation and renewals, and produces board reporting on progress.
- DeepReview can re-assess the acquired public footprint from time to time, until it moves under your own.
A general guide to the technology side of a deal, not legal, tax or financial advice. Adapt it to the deal in front of you, and take advice where the stakes call for it.