MiddleMail

MiddleMail is an email sending middleware: It offers an API for transaction email delivery and activity logging and acts as a middleware for other delivery services. Because all parts of MiddleMail are pluggable it can be used in different configurations for both production and staging applications: E.g. you can turn off actual delivery for a staging deployment but leave activity logging enabled to view recent email activity.

Projects

Project	Package	Description
MiddleMail		Core library and abstractions
MiddleMail.Model		Message model shared by most other projects
MiddleMail.Server		Ready to use server application
MiddleMail.Client.RabbitMQ		Client library that uses RabbitMQ as a backend
MiddleMail.MessageSource.RabbitMQ	-	MessageSource implementation that uses RabbitMQ as a backend
MiddleMail.Delivery.Smtp	-	Delivery implementation via SMTP
MiddleMail.Storage.Memory	-	Activity storage in-memory
MiddleMail.Storage.ElasticSearch	-	Activity storage in ElasticSearch

Concepts

The three most important concepts in MiddleMail are MessageSource, Storage and Delivery.

A MiddleMail.IMessageSource defines how MiddleMail consumes emails. Those emails then enter the processing pipeline.

To persist information about email activity MiddleMail uses a MiddleMail.IStorage. Depending on the implementation this makes email activity easily searchable and debuggable.

For actual delivery an MiddleMail.IMailDeliverer is used: MiddleMail.Delivery.Smtp implements such a deliverer for SMTP but it is easy to plugin your prefered Email Delivery SaaS or disable delivery for debugging and testing.

Configuration

The following table lists the configurable parameters for MiddleMail. To pass them as environment variables on bash replace : with __.

Parameter	Description
MiddleMail:Delivery:Smtp:Server	Hostname of the upstream SMTP server
MiddleMail:Delivery:Smtp:Port.	Port of the SMTP server
MiddleMail:Delivery:Smtp:Username	Username for the SMTP connection
MiddleMail:Delivery:Smtp:Password	Password for the SMTP connection
MiddleMail:Delivery:MimeMessage:MessageIdDomainPart	Domain part of the message id as in <[email protected]> used to construct the message id of a mime message.
MiddleMail:ExponentialBackoff:Multiplicator	delay = 2^iteration * multiplicator seconds delay after processing failure.
MiddleMail:Storage:ElasticSearch:Uri	URI of the Elasticsearch instance
MiddleMail:Storage:ElasticSearch:Index	name of the Elasticsearch index we write messages to
MiddleMail:MessageSource:RabbitMQ:ConnectionString	Connectionstring to rabbitmq, as defined at https://github.com/EasyNetQ/EasyNetQ/wiki/Connecting-to-RabbitMQ. E.g. host=localhost;prefetchcount=10
MiddleMail:MessageSource:RabbitMQ:SubscriptionId	Unique subscription id for this instance of middle mail
REDIS_CONFIGURATION	Configuration used to connect to Redis, as defined at https://stackexchange.github.io/StackExchange.Redis/Configuration
REDIS_INSTANCE_NAME	The Redis instance name
DISABLE_SMTP	Do not actually send anything via SMTP.

Basic Local Setup

This setup assumes the use of Visual Studio Code as an editor. If not using VSCode, configure environment variables in whatever way is appropriate for your preferred launch mechanism. This setup also runs the dependencies in Docker. You don't have to do this, but it sure is convenient.

1. Clone this repository.
2. Create a launch.json in which you configure the environment variables described above in the Configuration section. This launch.json should target the build of the MiddleMail.Server project, since that's the standalone process. You probably also need to create a tasks.json to run it, with a build task, but that's no different from the standard launch.json setup.
3. Run the docker-compose.dev.yml file to spin up dependency services. It mainly includes:

• A RabbitMQ container as an email message queue.
• An Elasticsearch container as a storage solution.
  • Note that if you're not using Elasticsearch, you can edit the services found in MiddleMail/Server/Program.cs to replace ElasticSearchStorage in services.AddSingleton<IStorage, ElasticSearchStorage>(); with MemoryStorage, an in-memory storage solution. You will also need to edit the dependencies in MiddleMail.Server.csproj to depend on MiddleMail.Storage.Memory instead of MiddleMail.Storage.Elastic.
• A Redis container as a caching solution.
• An smtp4dev container as an SMTP server for development and testing.

1. Run the MiddleMailServer process (with your launch.json).
2. Optional: Test your new MiddleMail instance using the tools/EmailMessageGenerator project to send test emails.

Tools

Project	Description
EmailMessageGenerator	Generates test email messages