Before migrating an email to Google Groups by using the Groups Migration API, do the following
- Confirm that the target group exists and the group's email is accurate before migrating an email message to that group's archive. For more information about listing groups and users, see the Directory API.
- If the email's sender has the same domain as the target group, confirm the email sender exists before migrating the email message to the target group's archive.
- The email message format must be in the
  RFC 822 standard definition.
  Use the Content-type: message/rfc822header. Confirm that the email message'sTo:,From:, andDate:fields are properly formed. The response is returned in the JSON data format.
Migrate an email message to Google Groups
To migrate an email message to a group's archive, send a POST HTTP request,
include the Authorization header, and replace
GROUP_EMAIL_ADDRESS with the email address of the group that the messages
are intended for:
POST https://www.googleapis.com/upload/groups/v1/groups/GROUP_EMAIL_ADDRESS/archive?uploadType=media
Example request
This example migrates email messages to the samplegroup@googlegroups.com archive. The
Content-Length is limited to 25MB which includes the message's meta data, body, and any
attachments:
POST https://www.googleapis.com/upload/groups/v1/groups/samplegroup@googlegroups.com/archive?uploadType=media
Host: www.googleapis.com
Content-Type: message/rfc822
Content-Length: BYTES
Authorization: Bearer Auth token
METADATA_BODY
Replace the following:
BYTES: the number of bytes in the email.AUTH_TOKEN: the Authorization header.METADATA_BODY: the email's metadata, body, and any attachments.The following is an example email message in RFC 822 text format that was migrated into the
  archive of samplegroup@googlegroups.com. The NNNN@mail.samplegroup.com is this
  example's Message-ID. The migrated email's sender is samplesender@example.com and the email is
  migrated to the archive of the samplegroup@googlegroups.com group:
    Received: by 10.143.160.15 with HTTP; Mon, 16 Jul 2007 10:12:26 -0700 (PDT)
    Message-ID: <NNNN@mail.samplegroup.com>
    Date: Mon, 16 Jul 2007 10:12:26 -0700
    From: samplesender@example.com
    To: samplegroup@googlegroups.com
    Subject: SUBJECT
    MIME-Version: 1.0
    Content-Type: text/plain; charset=ISO-8859-1; format=flowed
    Content-Transfer-Encoding: 7bit
    Content-Disposition: inline
    Delivered-To: samplegroup@samplegroup.com
    This is the body of the migrated email message.
A successful response returns a 200 HTTP status code and the migration status.
For more information about responseCode values, see
  the Groups Migration API reference.
{
 "kind": "groupsMigration#groups",
 "responseCode": "SUCCESS",
}View imported messages on the Google Groups interface
On Google Groups, threads' read/unread state is stored separately for each user. When
  inserting messages and threads using the Groups Migration API, they're treated as if
  they were sent by the user in the From: header. This means that they appear as unread
  for all users, except for the user whose address is in the From: header. For example,
  after the previous JSON request example, the message titled SUBJECT appears as read
  if samplesender@example.com logged in to Google Groups, but appears as unread
  for all other users.