Sending emails in web applications

When you send emails from your web application, it’s often (usually) the case that there will be some change to the persistence layer. For example:

1. A new user registers for an account on your site – the new user is created in the database and an email is sent to them with a confirmation link
2. A user assigns a bug or issue to someone else – the issue is updated and email notifications are sent.

How you send these emails can be critical to the success of your application. How you send them depends on how important it is that the intended recipient receives the email.

We’ll look at the following four strategies in relation to the case where the mail server is down, using example 1.

TRANSACTIONAL & SYNCHRONOUS
The sending of the email fails and the user is shown an error message saying that their account could not be created. The application will appear to be slow and unresponsive as the application waits for the connection timeout. The account is not created in the database because the transaction is rolled back.

TRANSACTIONAL & ASYNCHRONOUS
The transactional definition here refers to sending the email to a JMS queue or saving it in a database table for another background process to pick up and send.

The user account is created in the database, the email is sent to a JMS queue for processing later. The transaction is successful and committed. The user is shown a message saying that their account was created and to check their email for a confirmation link. It’s possible in this case that the email is never sent due to some other error, however the user is told that the email has been sent to them. There may be some delay in getting the email sent to the user if application support has to be called in to diagnose the email problem.

NON-TRANSACTIONAL & SYNCHRONOUS
The user is created in the database, but the application gets a timeout error when it tries to send the email with the confirmation link. The user is shown an error message saying that there was an error. The application be slow and unresponsive as the it waits for the connection timeout

When the mail server comes back to life and the user tries to register again, they are told their account already exists but has not been confirmed and are given the option of having the email re-sent to them.

NON-TRANSACTIONAL & ASYNCHRONOUS
The only difference between this and transactional & asynchronous is that if there is an error sending the email to the JMS queue or saving it in the database, the user account is still created but the email is never sent until the user attempts to register again.