for SO https://stackoverflow.com/questions/51466729/mastransit-publish-vs-send-and-how-to-manage-message

gistfile1.txt

Gist because SO Rep system doesn't like me...

Just a bit of advice with the Email Service. We have a generic Emailer Consumer. This only accepts a Command. So we made a contract similar to:

public interface SendEmail
{
    IList<IEmailAddress> To { get; }
    IList<IEmailAddress> Cc { get; }
    IList<IEmailAddress> Bcc { get; }
    IEmailAddress From { get; }
    IEmailAddress ReplyTo { get; }
    string Subject { get; }

    // Can have multipary email bodies, hence the list.
    IList<IContent> Body { get; } // IContent is two properties {type: "", value: ""}
}
public interface IEmailAddress
{
    string Email { get; }
    string Name { get; } // display name
}
public interface IContent
{
    string Type { get; } // mimetype eg. text/plain, or text/html
    string Value { get; } // actual text, or html
}

so now, my application might publish events when things happen (notice they are past tense):
UserCreated
OrderShipped

And so I may have multiple Receive Endpoints, which will subscribe to those events

UserCreatedEmailConsumer
OrderShippedEmailConsumer

And each of those consumers will query the database, and get the e-mail Template, all the information related to those events, and populate the: to, from, subject, substitute into the email template from the db, then it will issue a _sendEndpoint.Send(...). This will send a command to the SendEmailConsumer which will perform the actual send using your e-mail provider (whether it is your own in house SMTP, or a 3rd party like Sendgrid, MailGun, Sparkpost, etc...).

This is also a nice structure, because you have the ability to configure within your SendEmailConsumer, First level and Second Level retries (based on transient failures=network blip, or an outage window=sendgrid id doing a 3 hour maintenance).

Additionally, keeping the SendEmail contract generic, you can switch mail provider anytime in the future by only changing the SendEmailConsumer.