Get weekly newsletters that only differ slightly, e.g. with a list of upcoming events? Forward your emails to email-diff, and it will reply with differences highlighted.

As of Jan 2020, this service runs well within the perpetually-free tiers of the hosting services it uses.

• email-diff is a Serverless Framework app, powered by AWS Lambda.
• The serverless database FaunaDB stores a copy of the last email it received.
• Mailgun sends and receives emails.

1. Create an AWS account: https://aws.amazon.com/
2. Create credentials and config files per the docs.

1. Create a serverless.com account.

2. Install the Serverless client, and log in

    npm install -g serverless
    npm install --save-dev serverless-ruby-package
   
    sls login
   

3. Customize serverless.yml to suit your needs. The AWS provider region should match the region specified in AWS config file.

4. Deploy, and note the function endpoint URL (ends with /email-diff/{id}).

    sls deploy
   

FYI: The ruby runtime is not currently supported by the Serverless Dashboard (monitoring).

1. Create a mailgun.com account
2. Enter a credit card to use the free plan without limitations on recipients and domains.
3. (Optional) On the dashboard, set up an MX on a subdomain as a sending domain. Alternatively, use the free sandbox subdomain provided by Mailgun.
4. Add a Receiving route for each recurring email you'd like to compare (e.g. 1 for each newsletter series).
   • Expression type: match recipient
   • Recipient type: (make up an email address that uses your sending domain)
   • Forward: (checked) Paste the endpoint URL from the serverless deployment, replacing {id} with a custom identifier (alphanumeric with dashes or underscores) corresponding to the email series being compared.
   • Store and notify: (not checked)
   • Stop: (checked)
5. Set MAILGUN_DOMAIN and MAILGUN_API_KEY in your environment to the appropriate values.

1. Create a fauna.com account.
2. From the dashboard, create a new database with name email-diff (or customize via ENV var FAUNA_DB_NAME).
3. Create a new collection with name email_version, with no TTL. Do Create collection index.
4. Under Security, Create a new key. Use Role: Server, Key Name: email-diff
5. Set FAUNA_DB_KEY in your environment to the key's secret value.

(optional)

1. Create a sentry.io account.
2. Create a new Ruby project
3. Set SENTRY_DSN in your environment to your project's DSN configuration value.

Have these variables set in your environment when deploying

• FROM_EMAIL: sending email address on sending domain
• RECIPIENTS: comma-separated email addresses, optionally in the form Sender Name <[email protected]>, [email protected]

• FROM_EMAIL
• MAILGUN_DOMAIN
• MAILGUN_API_KEY
• FAUNA_DB_KEY
• RECIPIENTS
• SENTRY_DSN

Install Ruby dependencies:

bundle install --standalone

Test integration locally:

rake test:integrated

Test on remote server:

sls invoke -f email-diff