GoBridge

GoBridge is an SMTP to GMail API service. It will allow you to host an SMTP server that will accept emails and directly INSERT them into users' inboxes, bypassing any filtering. This is achieved by using the GMail API; and specifically the users.messages.insert endpoint.

You will need to create and authorize a service account, save the service_secret.json file to the working directory, and delegate domain-wide authority for the service account. This will give permission to impersonate any user and insert the email into their inbox. For a step by step list of instructions please see GMailSetup.md

Package Installation

Run pip3 install -r requirements.txt to install the appropriate packages.

Configuration

Appropriate settings can be defined in the config.json file. The default values are:

[GOBRIDGE]
ClientSecretFile = service_secret.json
SMTPPort = 2500
SMTPInterface = localhost
Labels = INBOX,UNREAD,IMPORTANT,STARRED

The Labels section refer to GMail labels - the default values ensure the email will be as visible as possible to the user.

Make sure the service_secret.json file has been generated and downloaded.

Running

Simply run the Python file, for example:

$ python3 GoBridge.py

   _____       ____       _     _            
  / ____|     |  _ \     (_)   | |           
 | |  __  ___ | |_) |_ __ _  __| | __ _  ___ 
 | | |_ |/ _ \|  _ <| '__| |/ _` |/ _` |/ _ \
 | |__| | (_) | |_) | |  | | (_| | (_| |  __/
  \_____|\___/|____/|_|  |_|\__,_|\__, |\___|
                                   __/ |     
                                  |___/

                     SMTP to GMail API Server
                     V0.1

[+] Running GoBridge SMTP server on port  2500
[+] Successfully inserted message for glenn@widgets.com with Id: 186b32c792dcd88e
[+] Successfully inserted message for hazel@widgets.com with Id: 186b32c82342242f
[+] Successfully inserted message for brie@widgets.com with Id: 186b32c8abc5f0b0
[!] An error occurred inserting mail for nosuchuser@widgets.com: invalid_grant: Invalid email or User ID
[!] An error occurred inserting mail for glenn@baddomain.com: invalid_grant: Invalid email or User ID

As can be seen in the above output email addresses not in the scope of the service account will be rejected.

Docker build

In order to build docker image, need to run docker build -t GoBridge .

Docker running

To run GoBridge into docker image, need to set up few variables specify into .env.example

• First need to copy .env.exampke into .env file cp .env.example .env
• Run cat service_secret.json|base64 and copy value and set value of GOOGLE_SECRET_BASE64_ENCODED with output value

Now you can run docker run -p 2500:2500 -t --env-file=.env GoBridge

References:

https://developers.google.com/gmail/api/reference/rest/v1/users.messages/insert https://console.cloud.google.com/iam-admin/serviceaccounts https://developers.google.com/identity/protocols/oauth2/service-account#creatinganaccount https://developers.google.com/cloud-search/docs/guides/delegation#python https://stackoverflow.com/questions/42438902/gmail-api-user-impersonation-python