Why not estimate duration from bandwidth alone?

Mailbox migrations are throttled by source-side concurrency limits per IP address, IMAP command latency and auth controls — not just network capacity.

Why does adding VMs always reduce duration in this model?

Each VM runs on a dedicated public IP. Source platforms enforce limits per IP, not per global session. So every extra VM brings a fresh independent quota — throughput scales linearly with VM count.

What is a delta sync?

A short pass run after bulk copy to capture messages received during the migration window, before the DNS cutover.

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Source platform

Mailboxes

Average size / mailbox (GB)

Virtual machines 1 VM = 1 IP

Operating hours / day

Estimated project duration —

Bulk copy window —

Total volume —

Effective throughput —

Active workers —

Public IPs needed —

VM overhead cost —

Prep

Copy

Delta

Load per IP — / — workers/IP

Platform note

Model assumptions

Conservative planning benchmarks — not vendor commitments. Real throughput depends on auth configuration, latency and mailbox state.

Source	Speed / worker	Max workers / IP	Workers / VM Scale = VMs × min(wpvm, wip)
Gmail / Google Workspace	1.8 GB/h	8	12 (×VM)
Microsoft 365	2.8 GB/h	12	16 (×VM)
Gandi Mail	2.4 GB/h	8	12 (×VM)
Zimbra	3.0 GB/h	12	14 (×VM)
OVH / Hosted Exchange	2.6 GB/h	10	12 (×VM)
IMAP générique	3.5 GB/h	20	20 (×VM)

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