System Migration After Acquisition: CRM, ERP, Email, HR, and Operational Tools

Every integration involves migrating systems. And every migration contains traps for the unprepared.

According to Gartner, 83% of data migration projects fail or exceed their budget and timelines. KPMG estimates an average budget overrun of $300,000 per data set in failed migrations.

This isn't because migration is impossible. It's because the non-obvious problems (the structural mismatches, the Conversion Trap, the process vs. data gaps) catch teams who thought they were prepared.

This article covers the principles and pitfalls for the core systems: email, CRM, ERP, HR, and operational tools. Not every platform or scenario, but the things that derail otherwise solid plans.

This article is adapted from Chapter 6 of The Roll-Up Integration Playbook, our free guide to post-merger technical integration.

Migration Sequencing: Why Order Matters

The order you migrate systems matters. Some migrations create dependencies for others. Some are lower risk and good for building confidence before tackling harder ones.

Typical Sequence

OrderSystemTimeframeRationale1Email & IdentityDays 1-30Security perimeter, affects everyone, relatively straightforward2CRMDays 30-60Sales visibility, customer data unified early, tests migration process3Finance/ERPDays 45-90Requires fiscal calendar alignment, parallel running4HR & PayrollDays 30-60Often parallel with CRM, driven by payroll cycles5Operational SystemsDays 60-90+Most complex, benefits from earlier lessons, may stay separate

Why This Order Works

Email and identity come first because they affect everyone and establish your security perimeter. They're also relatively low risk compared to business systems.

CRM comes next because sales visibility is critical and you want customer data unified early. It's also a good test of your migration process before tackling finance.

Finance waits for a natural cutover point (month-end, quarter-end) and requires more preparation. It often runs parallel with later stages of CRM migration.

HR can run parallel with CRM since they're largely independent systems. Timing may be driven by payroll cycles.

Operational systems come last because they're often the most complex and benefit from lessons learned on earlier migrations.

When to Deviate

• If finance reporting is your biggest pain point, ERP may come earlier
• If the acquired company's CRM is actively losing deals, that becomes urgent
• If security concerns are severe, you might do a Day 1 email cutover
• If operational systems are simple, they might move earlier

Let your business priorities drive the sequence, not a rigid playbook. For the overall execution timeline, see The First 100 Days After an Acquisition.

Email and Identity: The Conversion Trap

Email migration seems simple. It rarely is.

The platform decision isn't always obvious. If you're on Microsoft 365 and they're on Google Workspace, migration seems straightforward. But if they're a small team who lives in Google Docs, forcing them onto Microsoft may create more friction than it's worth.

The real danger is the Conversion Trap.

What the Conversion Trap Looks Like

When migrating from Google Workspace to Microsoft 365, Google Docs, Sheets, and Slides must be converted to Office formats. This sounds simple but causes real problems:

Google FeatureWhat Happens in ConversionComplex formulas with IMPORTRANGEBreaks completelyGoogle Apps ScriptsStops runningEmbedded links to other Google filesBroken referencesHeavy formatting in Google DocsMay not convert cleanlyQuery functions in SheetsOften fail or produce errors

Before migration, scan for complex files that need manual remediation. Don't discover these problems on migration day.

Example: The Spreadsheet That Runs the Business

An acquired company has a Google Sheet that pulls data from three other sheets using IMPORTRANGE, calculates sales commissions with custom formulas, and triggers email notifications via Google Apps Script. It's ugly but it works, and the sales manager depends on it.

When you migrate to Microsoft 365, this sheet becomes a broken Excel file. The IMPORTRANGE functions fail. The Apps Script stops running. The formulas may convert incorrectly. Nobody told you this spreadsheet existed because "it's just a spreadsheet."

Before any email/identity migration, audit for these dependencies. The "simple" migration becomes complex when you discover what people have built on top of the platform.

Timing: Email migration typically takes 2-4 weeks from planning to completion. If doing Day 1 cutover for security reasons, preparation must happen pre-close.

CRM: Data Quality and Structural Mismatches

CRM migration is often the highest-risk migration for business disruption. Get it wrong and your sales team loses visibility, deals fall through cracks, and customer relationships suffer.

The Data Quality Reality

Expect problems. Research shows that data quality issues affect most migrations:

• Duplicate records - the same customer entered multiple times
• Incomplete data - required fields empty or filled with placeholders
• Outdated information - contacts who left years ago
• Inconsistent formatting - phone numbers, addresses, names entered differently

Budget significant time for data cleanup before migration. A "quick" CRM migration that skips cleanup becomes a slow migration when you're fixing problems post-go-live.

Deloitte research shows that 32% of executives identify data integration as the single biggest challenge in M&A. CRM is where this challenge is most visible.

Process vs. Data Mismatch

The bigger challenge is often process, not data. The acquired company's sales process may be fundamentally different from yours:

• They might track different pipeline stages
• They might use different fields
• They might define "opportunity" differently
• Their lead qualification criteria might not match yours

Simply migrating data from their system to yours doesn't solve this. You need to decide:

• Are they adopting your process?
• Are you creating a hybrid?
• Are you running separate processes within one system?

Make these decisions before migration, not during.

Example: HubSpot to Salesforce

This is one of the most common CRM migrations, and it's more complex than it appears.

HubSpot ConceptSalesforce ConceptThe ProblemCompanies & ContactsAccounts & ContactsHubSpot allows flexible associations; Salesforce has stricter parent-child hierarchyDealsOpportunitiesStage definitions, pipeline structures, and required fields are completely differentActivity trackingActivitiesData stored in different structuresCustom propertiesCustom fieldsDifferent data types, picklist values need recreation

The result: you can't just export from HubSpot and import to Salesforce. You need field mapping, data transformation, decisions about structural differences, and often significant data cleanup in between.

Timing: CRM migrations typically take 8-12 weeks including data cleanup and training. Simple migrations (clean data, similar processes) can be faster. Complex ones take longer.

Finance and ERP: Parallel Running and Dimensional Mismatches

Finance migration keeps CFOs up at night, and for good reason. Errors in financial data have regulatory implications, affect reporting to investors, and can take months to untangle.

Parallel Running Is Essential

For finance systems, run both systems in parallel until you're confident the new system is producing accurate results. This typically means:

• Both systems active for at least one full accounting period
• The same transactions entered in both (or one system feeding the other)
• Reports generated from both and reconciled
• Cutover only when outputs match consistently

Yes, this is extra work. It's also how you avoid a financial reporting disaster.

Research shows that only 57% of successful acquirers fully integrate systems and processes. For finance, partial integration without proper parallel running is how errors compound.

Chart of Accounts Alignment

The Chart of Accounts (CoA) is where technical migration meets business decisions. The acquired company's CoA won't match yours.

Mapping between them requires decisions about:

• How to categorise revenue and expenses
• What level of detail to maintain
• How to handle historical data under old categories

This isn't a purely technical exercise. Finance leadership needs to drive CoA mapping decisions. Start early because these conversations take longer than expected.

Example: Xero to NetSuite

A common scenario: your platform runs NetSuite, and you acquire a company on Xero. Both are accounting systems. How hard can migration be?

XeroNetSuiteThe GapFlat chart of accountsMulti-dimensional (account + class + department + location + custom segments)NetSuite's power doesn't exist in XeroTracking categories (limited)Full dimensional reportingDon't map cleanlyBank reconciliation methodDifferent reconciliation approachProcess change requiredMulti-currency handlingMore complex multi-currencyTransformation neededSimple tax codesMore granular tax configurationMapping required

The decision: do you flatten NetSuite to match how Xero worked (losing reporting capability), or do you enrich historical data with dimensions it never had (requiring business decisions about how to categorise old transactions)?

The chart of accounts mapping alone typically requires several sessions with finance leadership. Then you need to transform the data, validate it, and run parallel periods to ensure the numbers match.

Timing: ERP migrations take 12-20 weeks and should align with fiscal calendar. Month-end or quarter-end cutovers are typical. Year-end is ideal if timeline permits. Coordinate with auditors if relevant.

HR, Payroll, and Operational Systems

A few critical points on these systems:

HR and Payroll

Payroll accuracy is non-negotiable. People notice when their pay is wrong. Run parallel payroll calculations before cutover, verify tax codes and pension contributions, and have a rollback plan.

The hidden complexity is policy harmonisation:

• Different leave accrual methods
• Different leave years
• Different pension schemes
• Different benefits structures

You can't just migrate the data. You need HR and legal decisions about how to align policies first. The technical migration follows the business decisions.

Under GDPR, employee data requires legitimate basis for processing. Don't migrate more than you need.

Operational Systems

Not every operational system needs to migrate.

If the acquired company runs specialist software that genuinely works for them, consider keeping it separate and integrating at the data layer via API. Jobs and invoices can flow into your finance system for unified reporting without forcing everyone onto a single platform.

The risk is accumulating technical debt: too many systems connected by custom integrations.

Use a Sunset Policy to ensure these decisions are revisited. For the framework, see How to Decide the Right Integration Level for Each Acquisition.

When to Bring in Specialists

Not every migration needs external help. But some are complex enough that specialist expertise pays for itself in speed and reduced risk.

Consider Specialists When

SituationWhy Specialists HelpPlatform complexityEnterprise platforms (Salesforce, NetSuite) where configuration expertise mattersData complexityLarge datasets, complex transformations, significant cleanup requiredIntegration complexityMultiple systems with dependencies, custom API work neededTime pressureAggressive timeline where parallel effort accelerates deliverySkill gapsTeam lacks experience with specific platforms or migration patternsRisk sensitivityFinance or other high-stakes migrations where errors are costly

Keep In-House When

• Small, straightforward migrations with clean data
• Your team has genuine experience with the platforms involved
• Timeline is flexible enough to learn as you go
• The migration is mostly configuration, not complex data work

The Hybrid Model

Most mid-market integrations use a mix:

• Internal team owns project management, business decisions, and user communication
• Specialists handle technical migration work for complex systems

This gives you control without requiring deep technical expertise in every platform.

For more on resourcing options, see In-House, Contractors, or Partners: Who Should Handle Post-Merger Integration?.

Key Takeaways

• Sequence matters. Email/identity first, then CRM, then finance, then HR, then operational systems. Deviate based on business priority, not convenience.
• Watch for the Conversion Trap. Google Docs with complex formulas or scripts will break when converted to Office formats. Scan and remediate before migration.
• CRM data is messier than you think. Budget significant time for cleanup. Process alignment is often harder than data migration.
• Parallel running is mandatory for finance. Run both systems for at least one full period before cutover. Coordinate with fiscal calendar and auditors.
• Not every system needs to migrate. Keeping operational systems separate while integrating via API can preserve value while providing visibility.
• Know when to bring in specialists. Complex platforms, large datasets, tight timelines, and high-stakes migrations often justify external expertise.

Get the Full Playbook

This article covered system migration principles and pitfalls. For the complete guide, including the 100-day execution timeline, training and adoption guidance, and ready-to-use checklists, download The Roll-Up Integration Playbook.

Download the Playbook

About PMI Stack

PMI Stack helps small-to-mid cap roll-ups unify systems, data, and workflows across their acquired companies. We specialise in the technical side of post-merger integration: data migration, system consolidation, and the change management that makes new tools stick.

If you're planning a system migration and want to talk through your specific situation, book a free discovery call.

Statistics cited from Gartner, KPMG, Deloitte, and PwC. For the full research compilation, see 50+ Post-Merger Integration Statistics (2026).