google-group-import.sh

#!/bin/bash

function usage() {
        (
        echo "usage: $0 <auth-token> <group-address> <mbox-dir>"
        echo "To generate an auth token go to https://developers.google.com/oauthplayground/ and get an access token for Google Groups migration"
        ) >&2
        exit 5
}

AUTH_TOKEN="$1"
shift
GROUP="$1"
shift
MBOX_DIR="$1"
shift

[ -z "$AUTH_TOKEN" -o -z "$GROUP" -o -z "$MBOX_DIR" ] && usage

for file in $MBOX_DIR/*; do
        curl -H"Authorization: Bearer $AUTH_TOKEN" -H'Content-Type: message/rfc822' -X POST \
                "https://www.googleapis.com/upload/groups/v1/groups/$GROUP/archive?uploadType=media" --data-binary @${file} || exit 1
done

I've upgraded it so that even if it fails halfway, you can resume your import. All emails that are to be imported must be children of the folder specified, sub-folders are not included because this script creates a sub-folder of successful for those that worked and leaves the ones that doesn't in the directory, errors will show in console.

This worked marvelously for me for thousands of emails, even if the auth token expired.

#!/bin/bash

function usage() {
        (
        echo "usage: $0 <auth-token> <group-address> <mbox-dir>"
        echo "To generate an auth token go to https://developers.google.com/oauthplayground/ and get an access token for Google Groups migration"
        ) >&2
        exit 5
}

AUTH_TOKEN="$1"
shift
GROUP="$1"
shift
MBOX_DIR="$1"
shift

[ -z "$AUTH_TOKEN" -o -z "$GROUP" -o -z "$MBOX_DIR" ] && usage

SUCCESS="$MBOX_DIR/successful"

mkdir -p $SUCCESS

success_count=0
failure_count=0

for file in $MBOX_DIR/*.eml; do
	if curl --fail -H"Authorization: Bearer $AUTH_TOKEN" -H'Content-Type: message/rfc822' -X POST "https://www.googleapis.com/upload/groups/v1/groups/$GROUP/archive?uploadType=media" --data-binary "@$file"; then  
		mv "$file" $SUCCESS
		success_count=$((success_count + 1))
	else
		failure_count=$((failure_count + 1))
	fi
done

echo "Done. $success_count successfully imported, $failure_count failed."

I've found https://github.com/XaviTorello/mail2googlegroup

Recommend changing --data-binary @${file} to --data-binary @"${file}" to fix issues with files having spaces.