400 Bad Request (Importing Gmail) – CloudM

Platform

Source - Any, including Google Workspace > Destination - Google Workspace (Mail)

Error

400 Bad Request

This is specific to individual mail item failures, visible in CloudM Migrate during migration via Progress > Import Failures, or the HTML report 'Import Failures' post-migration.

If a user migration fails outright with a similar error, it should be logged in a support ticket here.

Diagnosis

This is a Google error and is typically caused by data that cannot be imported into Gmail for one of the following reasons:

Blocked attachment types which are not allowed in Gmail per https://support.google.com/mail/answer/6590
Emails containing virus attachments
Emails not conforming to RFC 822 per https://www.ietf.org/rfc/rfc2822.txt

Solution

The above are the most popular reasons for the error, and there is no solution to get the items into Gmail as it simply will not accept them,
It can very rarely, however, also be a temporary error being thrown by Google. In which case, remigrating might resolve it.

It's important to note, that the more frequent this error, the slower a migration will run, as it will retry each failing message per the configuration step (2) Destination Platform - Google Workspace > Advanced Settings > Transfer Settings > Retry Count.