Outlook to Gmail Migration
Migration Paths
Assess the source environment first:
| Source |
Best Method |
Scope |
| Office 365 / Exchange Online |
Google Data Migration Service (Admin Console) |
Org-wide, bulk |
| On-prem Exchange |
GWMMO tool or IMAP migration |
Per-user or bulk |
| PST files |
GWMMO tool or Outlook IMAP bridge |
Per-user |
| Outlook.com (personal) |
IMAP migration in Admin Console |
Per-user |
Pre-Migration Checklist
Run through this with the client before touching anything:
- Inventory — Number of users, total mailbox sizes, largest mailbox, shared mailboxes, distribution lists
- Google Workspace plan — Confirm active subscription, verify admin access (Super Admin required)
- Source admin access — Global Admin (O365) or Exchange Admin + app passwords
- DNS access — Whoever manages MX records (registrar, Cloudflare, etc.)
- Data scope — Email only? +Contacts? +Calendars? +Drive files?
- Cutover window — When to switch MX records (weekend recommended)
- Client communication — Draft email to users about the switch, new login instructions
- Retention — Keep source mailboxes active 30 days post-migration as safety net
Method 1: Google Data Migration Service (Recommended for O365)
Best for org-wide migrations from Exchange Online / Office 365.
Setup
- Google Admin Console → Data → Data import & export → Data Migration (New)
- Select Microsoft Office 365 as source
- Click Connect → sign in as Microsoft Global Admin → grant permissions
- Select what to migrate: Email, Contacts, Calendars
- Choose date range filter (optional — migrate only last N months to save time)
Execution
- Add users to migrate (CSV upload for bulk:
source_email,destination_email)
- Start migration — Google handles delta sync automatically
- Monitor progress in Admin Console → shows per-user status
- Migration runs in background — users can keep using Outlook during this phase
CSV Format
source_email,destination_email
john@company.onmicrosoft.com,john@company.com
jane@company.onmicrosoft.com,jane@company.com
See references/csv-template.md for full template with notes.
Method 2: GWMMO Tool (PST / Outlook Profile)
Best for individual users or PST file imports.
- Download GWMMO: https://tools.google.com/dlpage/gsmmo/
- Install on machine with Outlook profile or PST access
- Sign in with Google Workspace account
- Select Outlook profile or browse to PST file
- Choose data: Email, Contacts, Calendars, Junk
- Start import — progress shown in tool
Limitations: Runs per-user, requires desktop access, Windows only.
Method 3: IMAP Bridge (Manual / Small Scale)
For personal Outlook.com accounts or when other methods fail:
- Enable IMAP in Gmail: Settings → Forwarding and POP/IMAP → Enable IMAP
- In Outlook desktop, add Gmail as IMAP account
- Drag-and-drop folders from Outlook mailbox to Gmail IMAP folders
- Slow but works for any IMAP-capable source
DNS / MX Cutover
After migration data is transferred:
- Verify domain in Google Admin Console (TXT record)
- Update MX records to Google:
Priority Host
1 ASPMX.L.GOOGLE.COM
5 ALT1.ASPMX.L.GOOGLE.COM
5 ALT2.ASPMX.L.GOOGLE.COM
10 ALT3.ASPMX.L.GOOGLE.COM
10 ALT4.ASPMX.L.GOOGLE.COM
- Set SPF:
v=spf1 include:_spf.google.com ~all
- Set DKIM: Admin Console → Apps → Gmail → Authenticate email → Generate DKIM
- Set DMARC:
v=DMARC1; p=none; rua=mailto:admin@domain.com (start with p=none, tighten later)
- TTL: Lower TTL to 300 before cutover, restore to 3600 after 48h
See references/dns-records.md for copy-paste DNS templates.
Post-Migration Validation
Run these checks for every user:
See references/validation-checklist.md for printable per-user checklist.
Common Issues
| Issue |
Fix |
| Migration stuck at 0% |
Re-authorize source admin credentials |
| Missing folders |
Google flattens deep nesting → becomes labels |
| Calendar recurring events broken |
Re-create manually (known Google limitation with complex recurrences) |
| Contacts duplicated |
Use Google Contacts merge duplicates tool |
| Large attachments missing |
Items >25MB not migrated — export separately |
| Shared mailbox not migrating |
Convert to Google Group or shared drive |
| MX propagation slow |
Check TTL, use dig MX domain.com to verify |
Deliverables Template
For client-facing migration projects, prepare:
- Migration Plan — Timeline, phases, user batches, rollback plan
- User Communication — Email template announcing the switch
- Admin Runbook — Step-by-step for the migration operator
- Validation Report — Per-user sign-off checklist
See references/client-templates.md for ready-to-use templates.
1---2name: outlook-to-gmail3description: Migrate email, contacts, and calendars from Microsoft Outlook (Office 365 / Exchange / PST) to Google Workspace (Gmail). Use when a user asks to migrate from Outlook to Gmail, transfer emails from Microsoft 365 to Google Workspace, import PST files to Gmail, switch from Exchange to Gmail, or plan an Office 365 to Google Workspace migration. Covers: single-user migrations, bulk/org-wide migrations, PST imports, calendar + contacts transfer, DNS/MX cutover, and post-migration validation.4---5
6# Outlook to Gmail Migration
7
8## Migration Paths
9
10Assess the source environment first:
11
12| Source | Best Method | Scope |
13|--------|------------|-------|
14| Office 365 / Exchange Online | Google Data Migration Service (Admin Console) | Org-wide, bulk |
15| On-prem Exchange | GWMMO tool or IMAP migration | Per-user or bulk |
16| PST files | GWMMO tool or Outlook IMAP bridge | Per-user |
17| Outlook.com (personal) | IMAP migration in Admin Console | Per-user |
18
19## Pre-Migration Checklist
20
21Run through this with the client before touching anything:
22
231. **Inventory** — Number of users, total mailbox sizes, largest mailbox, shared mailboxes, distribution lists
242. **Google Workspace plan** — Confirm active subscription, verify admin access (Super Admin required)
253. **Source admin access** — Global Admin (O365) or Exchange Admin + app passwords
264. **DNS access** — Whoever manages MX records (registrar, Cloudflare, etc.)
275. **Data scope** — Email only? +Contacts? +Calendars? +Drive files?
286. **Cutover window** — When to switch MX records (weekend recommended)
297. **Client communication** — Draft email to users about the switch, new login instructions
308. **Retention** — Keep source mailboxes active 30 days post-migration as safety net
31
32## Method 1: Google Data Migration Service (Recommended for O365)
33
34Best for org-wide migrations from Exchange Online / Office 365.
35
36### Setup
37
381. Google Admin Console → **Data** → **Data import & export** → **Data Migration (New)**
392. Select **Microsoft Office 365** as source
403. Click **Connect** → sign in as Microsoft Global Admin → grant permissions
414. Select what to migrate: Email, Contacts, Calendars
425. Choose date range filter (optional — migrate only last N months to save time)
43
44### Execution
45
461. Add users to migrate (CSV upload for bulk: `source_email,destination_email`)
472. Start migration — Google handles delta sync automatically
483. Monitor progress in Admin Console → shows per-user status
494. Migration runs in background — users can keep using Outlook during this phase
50
51### CSV Format
52
53```csv
54source_email,destination_email
55john@company.onmicrosoft.com,john@company.com
56jane@company.onmicrosoft.com,jane@company.com
57```
58
59See `references/csv-template.md` for full template with notes.
60
61## Method 2: GWMMO Tool (PST / Outlook Profile)
62
63Best for individual users or PST file imports.
64
651. Download GWMMO: https://tools.google.com/dlpage/gsmmo/
662. Install on machine with Outlook profile or PST access
673. Sign in with Google Workspace account
684. Select Outlook profile or browse to PST file
695. Choose data: Email, Contacts, Calendars, Junk
706. Start import — progress shown in tool
71
72**Limitations**: Runs per-user, requires desktop access, Windows only.
73
74## Method 3: IMAP Bridge (Manual / Small Scale)
75
76For personal Outlook.com accounts or when other methods fail:
77
781. Enable IMAP in Gmail: Settings → Forwarding and POP/IMAP → Enable IMAP
792. In Outlook desktop, add Gmail as IMAP account
803. Drag-and-drop folders from Outlook mailbox to Gmail IMAP folders
814. Slow but works for any IMAP-capable source
82
83## DNS / MX Cutover
84
85After migration data is transferred:
86
871. **Verify domain** in Google Admin Console (TXT record)
882. **Update MX records** to Google:
89 ```
90 Priority Host
91 1 ASPMX.L.GOOGLE.COM
92 5 ALT1.ASPMX.L.GOOGLE.COM
93 5 ALT2.ASPMX.L.GOOGLE.COM
94 10 ALT3.ASPMX.L.GOOGLE.COM
95 10 ALT4.ASPMX.L.GOOGLE.COM
96 ```
973. **Set SPF**: `v=spf1 include:_spf.google.com ~all`
984. **Set DKIM**: Admin Console → Apps → Gmail → Authenticate email → Generate DKIM
995. **Set DMARC**: `v=DMARC1; p=none; rua=mailto:admin@domain.com` (start with `p=none`, tighten later)
1006. **TTL**: Lower TTL to 300 before cutover, restore to 3600 after 48h
101
102See `references/dns-records.md` for copy-paste DNS templates.
103
104## Post-Migration Validation
105
106Run these checks for every user:
107
108- [ ] Email receiving on Gmail (send test from external)
109- [ ] Historical emails present (spot-check oldest + newest)
110- [ ] Folders/labels mapped correctly
111- [ ] Contacts imported (check count)
112- [ ] Calendar events present (check recurring events specifically)
113- [ ] Shared mailboxes / groups recreated as Google Groups
114- [ ] Signatures set up in Gmail
115- [ ] Mobile devices re-configured (Gmail app or IMAP)
116- [ ] Outlook desktop disconnected or reconfigured
117
118See `references/validation-checklist.md` for printable per-user checklist.
119
120## Common Issues
121
122| Issue | Fix |
123|-------|-----|
124| Migration stuck at 0% | Re-authorize source admin credentials |
125| Missing folders | Google flattens deep nesting → becomes labels |
126| Calendar recurring events broken | Re-create manually (known Google limitation with complex recurrences) |
127| Contacts duplicated | Use Google Contacts merge duplicates tool |
128| Large attachments missing | Items >25MB not migrated — export separately |
129| Shared mailbox not migrating | Convert to Google Group or shared drive |
130| MX propagation slow | Check TTL, use `dig MX domain.com` to verify |
131
132## Deliverables Template
133
134For client-facing migration projects, prepare:
135
1361. **Migration Plan** — Timeline, phases, user batches, rollback plan
1372. **User Communication** — Email template announcing the switch
1383. **Admin Runbook** — Step-by-step for the migration operator
1394. **Validation Report** — Per-user sign-off checklist
140
141See `references/client-templates.md` for ready-to-use templates.
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