Lightning Sync to Einstein Activity Capture: The 2026 Migration Guide

Lightning Sync to Einstein Activity Capture is no longer a project you can defer. If your org uses Lightning Sync with Microsoft 365 and Exchange Web Services, Salesforce says to migrate to Einstein Activity Capture before August 2026, then upgrade the Microsoft connection to Microsoft Graph by August 2026. Microsoft is disabling EWS in Exchange Online in October 2026, and Lightning Sync retires overall in April 2027. Treat this as a two-step cutover, not a single wizard run. (help.salesforce.com)

Two corrections before we go further, because most migration guides get these wrong:

Lightning Sync synced contacts and calendar events. It did not automatically capture email. What users remember as "email sync" was typically Outlook Integration, Inbox, or manual logging running alongside Lightning Sync. That matters because the migration tool moves Lightning Sync settings, while EAC's email capture is a separate architecture choice you still need to make. (resources.docs.salesforce.com)

The blanket advice that "EAC stores everything off-platform" is outdated in 2026. Event data synced through EAC is now stored on the Salesforce platform. Email can also be stored natively as EmailMessage and Task records if Sync Email as Salesforce Activity is enabled. Older EAC email configurations still use legacy capture, where emails appear on the Activity Timeline but are not standard Salesforce records, cannot be reported on, and age out under EAC retention rules. (help.salesforce.com)

The August 2026 Deadline: Why This Is a Forced Migration

Salesforce's guidance is direct: if Lightning Sync is connected to Microsoft Office 365 through EWS, migrate to Einstein Activity Capture before August 2026. That earlier date exists because Microsoft is retiring EWS for Exchange Online in October 2026. Salesforce lists April 2027 as the overall Lightning Sync retirement date, but Office 365 plus EWS customers are on the shorter clock. (help.salesforce.com)

There is also a sequencing problem that trips teams late in the project. The Lightning Sync migration tool moves your sync settings into EAC, but Microsoft 365 users stay on EWS until you complete the separate Microsoft Graph upgrade. Starting in Spring '26, new Microsoft 365 EAC setups use Graph automatically. Older Microsoft 365 EAC setups must be upgraded by August 2026, and there is no rollback to EWS after the upgrade. (help.salesforce.com)

For broader Microsoft-side planning — especially if your identity team owns the Graph cutover — pair this guide with EWS Shuts Down Oct 2026: The SaaS Guide to Microsoft Graph Migration.

Lightning Sync vs. Einstein Activity Capture: The Architecture Shift

This is the single most important thing to understand before you touch the migration tool.

Lightning Sync was a sync product for contacts and calendar events. It wrote data directly to standard Salesforce Contact and Event objects (and in some configurations, Task records). Those records were queryable via SOQL, available in reports, included in standard backups, and could fire Apex triggers and Flows. If you built automation on synced activities, it worked because the data was standard Salesforce records.

Einstein Activity Capture is a broader activity layer that syncs contacts and events and also captures email. But that single product name hides more than one storage model, and that is where admins get burned.

In 2026, EAC's architecture breaks down like this:

• Contacts sync to standard Contact records — same behavior as Lightning Sync.
• Events are now stored on the Salesforce platform as standard Event records. (help.salesforce.com)
• Emails are where behavior diverges. You have two modes:
  • Legacy capture (default for older EAC setups): Emails appear on the Activity Timeline but are stored on external infrastructure (Activity Platform / Hyperforce). They are not standard Salesforce records — no SOQL, no standard reports, no Apex triggers, no standard backups, and subject to rolling retention. (help.salesforce.com)
  • Sync Email as Salesforce Activity (available since Summer '25): Captured emails are written as native EmailMessage and Task records. They are queryable, reportable, trigger-capable, and follow your org's standard data retention. (help.salesforce.com)

Key Caveats for Native Email Sync

Before you flip the switch on Sync Email as Salesforce Activity, understand these trade-offs:

• Irreversible. Salesforce says you cannot revert from Sync Email as Salesforce Activity back to legacy capture. Model storage growth, duplicate behavior, and reporting needs before enabling it. (help.salesforce.com)
• Enhanced Email required. Your org must have Enhanced Email enabled.
• Storage impact. Every synced email consumes standard Salesforce data storage. If storage planning is not in your migration plan, it should be. (help.salesforce.com)
• Duplicate risk. When auto-sync is running, users can still manually log emails from Outlook or Gmail, creating duplicate records. The Activity Timeline may deduplicate in the UI while related lists and reports still show both copies. (help.salesforce.com)
• Historical backfill capped at 180 days. The migration to native email sync does not convert all legacy captured data.
• Older orgs may need to request activation or wait for broader self-service rollout. It is not automatically enabled.
• Email attachments are not captured as part of the sync. (help.salesforce.com)

What the Official Migration Tool Actually Does (And Doesn't Do)

The in-product flow is straightforward. Go to Setup → Lightning Sync, launch the migration tool, run the readiness check, move the settings, review the migrated EAC configuration, assign Einstein Activity Capture permissions, and turn off Lightning Sync. Salesforce says the tool summarizes the process up front and lets you pause after the readiness check if it finds issues. (help.salesforce.com)

What the tool handles

• Connection method
• Data types being synced (contacts, events, or both)
• Users and profiles assigned to each sync configuration
• Sync direction
• Sync filters, event series sync, and private event sync settings (help.salesforce.com)

What the tool does NOT handle

• Microsoft Graph upgrade. Microsoft 365 orgs that finish the settings migration are still on EWS until they complete the separate Graph upgrade. The tool is a settings migration, not a full auth migration.
• Email storage model choice. The tool does not choose between legacy email capture and Sync Email as Salesforce Activity. That is a separate architecture decision.
• Historical synced data. Events and Tasks already in Salesforce as standard records stay put. The tool does not reconcile the data architecture split going forward.
• Shared mailbox configurations. EAC ties authentication to individual user OAuth connections. Shared inboxes and forwarding rules are not supported.
• Custom sync filters with complex logic. Lightning Sync allowed per-user filter configurations that EAC's broader configuration model does not replicate.
• Automation dependencies. The tool has no awareness of Apex triggers, Flows, or Process Builder processes that fire on Task, Event, or EmailMessage creation. Depending on your email storage model, automations tied to standard record creation can fail silently.
• Retention, privacy, sharing, and storage side effects. These all require explicit decisions before go-live.

The migration tool gets you from A to B on configuration. Everything else — data architecture, automation continuity, compliance — is on you. For complex orgs, treat the wizard as step one. If anyone on the project treats the native wizard as proof that the migration is low risk, hand them The Data Migration Risk Model: Why DIY AI Scripts Fail and How to Engineer Accountability.

Edge Cases That Break Your EAC Migration

This is where most migrations go sideways. Each of these is a real scenario that breaks in production. Audit your org against every one of them before rollout.

1. Shared Mailboxes, Resource Calendars, and Delegated Accounts

EAC is account-centric. Salesforce says the connected email account must be the user's primary account on the Salesforce user record, must not be an alias, and must use UPN format. (help.salesforce.com)

Lightning Sync could sync shared calendars and resource calendars (conference rooms, team calendars). EAC does not support shared calendar sync, resource calendars, or delegated calendars. Sales reps who sent from or monitored shared inboxes (sales@company.com, support@company.com) were configurable under Lightning Sync. Under EAC, there is no way to capture activity from a shared mailbox in the standard configuration.

There is an extra trap: Salesforce documents that capture can work from connected mailboxes, but contact and event sync only works when the connected mailbox matches the Salesforce user's email. That is why delegated or secondary mailbox designs often look half-working in pilots — captured activity appears, but sync behavior does not line up with expectations. (help.salesforce.com)

Workarounds depend on the actual requirement. For shared visibility, Salesforce's native public calendars and resource calendars may suffice. For manual logging from delegated Outlook sources, the Outlook integration supports shared folders with limitations. For server-side capture into native Salesforce records with long retention, third-party tools like Revenue Grid or Riva position themselves specifically around this gap.

2. Microsoft Graph Is a Separate Project

The Graph upgrade is not part of the Lightning Sync migration tool. It is a separate workflow with separate owners and failure modes.

Starting in Spring '26, new Microsoft 365 EAC setups use Graph automatically. Older setups must be explicitly upgraded by August 2026, and there is no rollback to EWS after the upgrade. (help.salesforce.com)

Your Salesforce admin, Azure AD admin, and pilot users may all have work to do. The upgrade flow differs for org-level and user-level connections. If you also use Inbox, upgrading one side can upgrade the other. Leave enough calendar time for auth testing — last-minute identity surprises are what typically turn a one-week migration into a month-long incident.

3. On-Premises and Hybrid Exchange

One nuance most migration articles miss: on-prem Exchange is not automatically a blocker. Salesforce documents EAC support for Exchange Server 2013, 2016, and 2019 through a service account. (help.salesforce.com)

The real blocker is hybrid Exchange. Salesforce says hybrid deployments (mixed Exchange Online plus on-prem) are not supported. If your org has users split across Office 365 and on-premises Exchange, that topology needs to be resolved before you can commit to a clean migration path.

For purely on-prem Exchange organizations: EAC uses EWS with a service account to connect. Since Microsoft's EWS retirement applies specifically to Exchange Online, the on-prem EWS path may survive past October 2026 — but verify this against current Salesforce and Microsoft documentation before making commitments. Basic Authentication must be supported and enabled on the Exchange server.

4. Activity Automation Failures

Do not audit "activity automation" as a single bucket. Split it by Event, Task, EmailMessage, and any downstream process that reads activity reports.

• Events: In 2026, EAC events are native Event records on-platform. Event-triggered Flows, Apex triggers, reporting, and sharing logic should still work. Test explicitly in sandbox.
• Emails: Automation only sees EAC-generated data if Sync Email as Salesforce Activity is enabled. In legacy capture mode, emails are virtual activities — custom logic does not fire because there is no Salesforce record to act on.
• Duplicates: Native email sync introduces a different failure mode. Users can still manually log emails from Outlook or Gmail while auto-sync is running, creating duplicate records. The Activity Timeline may deduplicate in the UI while related lists and reports still show both copies. That discrepancy makes sales leadership think the migration is broken when the real issue is display behavior. (help.salesforce.com)

Audit triggers immediately:

SELECT Id, Name, TableEnumOrId 
FROM ApexTrigger 
WHERE TableEnumOrId IN ('Task', 'Event', 'EmailMessage')

If your metadata is in source control, run a code search before pilot week:

grep -R '<object>Task</object>\|<object>Event</object>\|<object>EmailMessage</object>' force-app/

Also audit Record-Triggered Flows and any surviving Process Builder artifacts on Task or Event objects. If you have automation that calculates last-activity-date rollups, updates Opportunity stages based on meeting counts, or fires follow-up sequences after email sync — test every path with pilot users in sandbox.

5. The Historical Data Split

Events and Tasks synced via Lightning Sync are standard Salesforce records. They remain in your org after migration. Once EAC takes over, the behavior depends on the storage model:

• Events: EAC events are now on-platform, so there is no architectural gap for calendar data going forward.
• Emails: If you stay on legacy capture, new email data goes to a different storage layer with rolling retention. If you enable Sync Email as Salesforce Activity, new emails become native records — but historical backfill is capped at 180 days.

If you run an Activity report after migration with legacy capture enabled, it will show a cliff where historical data stops and new data does not appear. Even with native email sync, the 180-day backfill limit creates a gap.

If your org already had EAC before Summer '25, Salesforce's Update & Migrate path can move previously captured email into native activity data. If your org never used EAC before, there is no Lightning Sync email history to convert — because Lightning Sync never captured email in the first place. (help.salesforce.com)

6. Matching Logic and CRM Data Quality

EAC's matching is email-address driven. It matches addresses from the From, To, and CC fields. With Sync Email as Salesforce Activity enabled, Salesforce can associate up to 50 unique email addresses per message, with one contact or lead record matched per address. On large accounts, that ceiling matters. (help.salesforce.com)

Legacy capture has another limit that surprises revenue teams: only emails from the first 50 directly related contacts are added to an Account record's Activity Timeline. On house accounts with many contacts, users see a partial account-level history and assume capture failed. (help.salesforce.com)

Contacts without a usable primary email are the obvious failure case. A quieter one: Salesforce notes that legacy capture can fail when Contact or Lead records mix standard and custom email address fields. If your org depends on custom people models, duplicate contacts, or custom-object matching, assume you need build work and pilot coverage — not just the wizard.

7. Aliases and UPN Mismatches

Salesforce says alias email addresses are not supported, and the connected account used for sync must match the Salesforce user's primary email in UPN format. (help.salesforce.com)

A documented failure mode: email and event capture appears to work, but contact and event sync does not, because the connected mailbox does not match the Salesforce user's email. These problems show up as "it works for some reps but not others." They are not random — they are identity and mailbox-design problems. (help.salesforce.com)

Map every pilot user to mailbox type, UPN, primary SMTP, alias usage, and connection method before rollout. If you skip that step, you will spend go-live week debugging identity drift instead of validating the target state.

8. Data Retention, Privacy, and Storage

Lightning Sync data persisted as standard records indefinitely. EAC's retention model is more complex:

• Legacy capture: Activity Platform retention ranges from 6 to 24 months depending on license. EAC Standard (included with Sales Cloud Starter, Professional, Enterprise, and Unlimited editions) defaults to 6 months with a cap of 100 users. The paid tier (Unlimited, Performance, or Sales Cloud Einstein add-on) defaults to 24 months and can be extended to 5 years via Salesforce Support. After the retention period, data is permanently deleted — it is not archived. (help.salesforce.com)
• Native email sync: Synced emails become standard Salesforce records and follow your org's data storage and retention model. No rolling deletion. But they consume standard Salesforce storage.

If you are in financial services, healthcare, or any regulated industry, evaluate these retention settings against your compliance policy before enabling EAC. Even the paid tier's 5-year maximum may not satisfy audit requirements in some jurisdictions.

Privacy behavior changes too. Legacy EAC has its own email-sharing and excluded-address controls. When Sync Email as Salesforce Activity is enabled, standard Salesforce activity sharing rules apply instead. Sensitive-email behavior also changes: native synced email discards emails flagged as sensitive or automated, while legacy EAC kept them private on the timeline. (help.salesforce.com)

Review your org's consent model, especially in jurisdictions covered by GDPR or CCPA. If you disable capture and later re-enable it, the system does not go back and fill the gap period. For more on compliance during migrations, see GDPR Compliant Data Migration: The Enterprise Blueprint.

The Pre-Migration Audit Checklist

Run through this before you touch the migration tool in production. The goal is to map every dependency before the wizard does what it does well: move settings.

Auth and topology:

• Which users are on Microsoft 365 with EWS?
• Which users are already on Graph?
• Which users are on Exchange Server 2013/2016/2019 on-prem?
• Does any team sit in a hybrid topology? (Hard blocker — stop there if yes.)

Lightning Sync configuration inventory:

• Document every sync config: sync direction, filters, event series/private event settings
• List assigned users and profiles for each config

EAC state inventory:

• Is EAC already enabled anywhere in the org?
• Is Sync Email as Salesforce Activity enabled?
• Was EAC turned on before or after Summer '25?

Automation inventory:

• Apex triggers on Task, Event, and EmailMessage objects
• Record-Triggered Flows on activity objects
• Process Builder artifacts still touching activities
• Validation rules, assignment logic, and downstream integration jobs reading activity data

Reporting inventory:

• Standard activity reports and dashboards
• Any dependency on Activity 360 report types or dashboard folders (being retired by Salesforce)

Mailbox pattern inventory:

• Shared mailboxes
• Resource calendars
• Delegate-managed calendars
• Alias-heavy users
• Secondary connected accounts

Data governance:

• Retention policy requirements for email and events
• Privacy and sharing model review
• Excluded domains and addresses
• Whether storage growth from native email sync is acceptable

Licensing:

• Verify Einstein Activity Capture license availability (EAC Standard is included with Sales Cloud editions, capped at 100 users with 6-month retention; full version requires Unlimited, Performance, or Sales Cloud Einstein add-on)
• Verify OAuth consent flow with Azure AD / Microsoft 365 admin

Use SOQL to quantify historical Lightning Sync record counts. Lightning Sync does not stamp one universal field, so start with the service account or sync user that created records in your environment:

-- Replace with your Lightning Sync integration user
SELECT COUNT()
FROM Event
WHERE CreatedById = '005XXXXXXXXXXXX'
 
SELECT COUNT()
FROM Contact
WHERE CreatedById = '005XXXXXXXXXXXX'

For a broader migration audit framework, see Salesforce Service Cloud Migration Checklist and Best Practices for CRM Data Migration in 2026.

Step-by-Step Migration Plan

This is the real-world 8-week version for a 50–500 rep org. The main rule: separate settings migration, auth migration, and behavior validation into different weeks so you can tell which layer failed.

Your pilot cohort should not be five average sellers. Include:

• One user on each mailbox topology (Microsoft 365, on-prem, alias-heavy)
• One exec or rep with delegate-managed scheduling
• One user tied to Event automation
• One seller on a large account with many contacts
• One team that depends on activity reporting for management review

Key Decisions to Make Now

Use this as a decision tree, not a discussion prompt:

Do you have Microsoft 365 users still on EWS? → Migrate to EAC and complete the Graph upgrade by August 2026. Do not wait for October. (help.salesforce.com)

Do you have on-prem Exchange users? → EAC supports Exchange 2013/2016/2019 via service account, but hybrid deployments are not supported. If you have a mixed topology, resolve it before committing to the migration. (help.salesforce.com)

Do you need email in reports, Flows, Apex, or downstream BI? → Enable Sync Email as Salesforce Activity. Legacy capture is not enough. Accept that the decision is irreversible and model storage growth first.

Do you have automation on Task/Event/EmailMessage objects? → Complete the full automation audit before rollout. Test every trigger and Flow in sandbox. Do not assume EAC-generated records behave identically to Lightning Sync records.

Do you use shared calendars or shared mailboxes? → Plan a workaround now. EAC does not support shared calendar sync. Evaluate Salesforce's native calendar, a custom Microsoft Graph integration, or a third-party tool.

Do you have compliance requirements for email retention? → Compare your retention policy against EAC's limits. Standard tier: 6 months. Paid tier: 24 months (extendable to 5 years). Native email sync: follows org retention. If your policy requires longer than 5 years and you must use legacy capture, you need an engineering solution.

Are you tight on Salesforce data storage? → Native email sync makes emails first-class records that consume storage. Model that before you enable it. (help.salesforce.com)

When to Bring in ClonePartner

The in-product Lightning Sync migration wizard handles the easy part: transferring configuration settings to EAC. For straightforward orgs with a single Office 365 tenant, no custom automation, and no shared calendars, the wizard is sufficient.

ClonePartner gets called in when the migration is blocked by topology or data model, not by clicking through Setup. That includes hybrid Exchange environments, alias-heavy mailbox designs, pre-Summer '25 EAC orgs that need a clean move to native email activity, and orgs where Task, Event, and EmailMessage logic fans out into Apex, Flow, BI, and downstream integrations.

We also handle cases where the historical model needs cleanup before cutover: consolidating activity-heavy reports, redesigning automations that assumed all activity lived on one object model, and building controlled workarounds for shared mailbox or resource-calendar workflows that EAC does not replace.

For compliance-heavy industries facing the data retention gap, we architect solutions to ensure long-term email and calendar audit trails remain intact, queryable, and compliant long after EAC's default deletion window expires.

Start the Clock Now

If you are on Microsoft 365 plus Lightning Sync with EWS, plan backward from August 2026 — not October and not "sometime before Spring '27." For an org with 200+ users, 6–8 weeks is the minimum for a controlled audit, pilot, remediation cycle, and phased rollout. Give yourself more time if you have hybrid Exchange, aliases, shared mailbox workflows, or heavy activity automation.

The migration tool exists. The documentation exists. But the edge cases — shared calendars, hybrid Exchange, broken automation, compliance gaps, the Graph upgrade — require planning that Salesforce's wizard cannot do for you.

Audit your org this week. Stand up a sandbox config next week. Everything after that is execution.

This guide reflects Salesforce and Microsoft documentation current as of June 2026. EAC's email architecture and Graph migration flow are still evolving, so recheck the latest release notes before final production cutover. (help.salesforce.com)