Moving Google Workspace mail to Microsoft 365: what happens to Gmail labels, and what you can leave out

Labels are not folders

Gmail has no folders. It has labels, and one message can carry several. Google's documentation says Gmail treats labels as folders for the purposes of IMAP, so an IMAP client sees each label as a folder, and a message ID lets a client identify a unique message across multiple folders. Outlook-style mailboxes in Microsoft 365 use folders, where a message normally lives in one. Microsoft's migration pages do not say how Gmail labels become folders or how a message with several labels is copied. Our reading, which a pilot mailbox should confirm, is that a copy which reads each label as a folder can meet the same message more than once, so folder counts can add up to more than the number of messages.

What Microsoft's migration moves

Microsoft documents a Google Workspace migration that can move mail and rules, calendar and contacts. Users must already exist as mail-enabled users, and mail-routing subdomains are needed on both sides. Rules arrive turned off, vacation and automatic reply settings are not migrated, and the largest single message is governed by the transport configuration, with a default of 35 MB. The documentation says a migration can take from several hours to a couple of days depending on the amount of data.

Microsoft also warns that retention and archive policies in the destination can make migrated items appear missing, and recommends disabling them before the migration. When the batch is started from Exchange Online PowerShell, an administrator can exclude folders by name and exclude messages by Gmail label. The Exchange admin center pages we read describe filtering by data type (mail, calendar, contacts and rules) and do not mention excluding folders or labels, so the exclusion control is a PowerShell one.

• Check which data types you need: mail only, or calendar and contacts too.
• Check retention and archive policies in the destination first.
• Check for messages over the size limit.

Decide what to leave out, then run a pilot

Write down what should happen to each kind of label. Microsoft documents one control: leaving folders out by name and leaving messages out by Gmail label. It does not document how labels are mapped to folders or how a message with several labels is copied, so there is no mapping to choose in advance; what arrives is observed on a pilot. Spam and trash usually should not be copied, and some labels are tags that may not be worth keeping, so choose what to leave out. Then copy one mailbox as a pilot, count what arrives, and locate a sample of messages that carried more than one label, and any that carried both a left-out and a kept label, because Microsoft does not say what happens to those either. If the same message appears in more than one folder, the options are to accept the duplicates, to leave a label out of the copy, or to tidy up afterwards as separate work.

• Which folders and labels to leave out, the one control Microsoft documents.
• What the pilot shows for messages with several labels, recorded before the rest are copied.
• If the pilot shows duplicates: accept them, leave a label out, or a separately quoted tidy-up.

Count, switch and keep the old mailbox

Compare folder and message counts per mailbox before and after, and explain every difference: an exclusion, a duplicate or a size limit. Switching MX records moves new mail only, and Microsoft notes that once you change the MX record all mail for the domain goes to Microsoft 365, so in our reading the users must be ready. Sync again as close to the switch as the batch allows, test mail in both directions after it, check the Google mailboxes for mail that arrived after the switch and bring it across, and leave them open and subscribed for a while. Remove the old provider's records from DNS only after mail is flowing.

How the paid outcome is accepted

The fixed-price job for this is a published test price of £395, not yet tested with buyers, payable after sign-off. It covers up to five mailboxes of up to 10 GB each, mail only, copied with a Microsoft migration batch started from Exchange Online PowerShell. Acceptance is a per-mailbox folder and message count comparison with every difference explained, a sample of 20 messages per mailbox located at Microsoft 365 with every folder holding a copy and every duplicate listed, a pilot note recording how multi-label messages arrived, and tests after the MX switch that new mail arrives and replies reach outside addresses. Calendars, contacts and files, licences and tenant creation are excluded, tidying duplicates is a separate quote, and no cut-over can promise zero delay for every sender.