What should a solutions architect do to meet these requirements?

Explanations:

Creating a separate application tier using EC2 instances dedicated to email processing adds complexity and operational overhead. It requires additional management of EC2 instances and scaling, which is not efficient given the goal of minimizing operational overhead.

Configuring the web instance to send emails through Amazon Simple Email Service (SES) is an effective solution as it is a fully managed email service that scales automatically and simplifies the process of sending marketing and order confirmation emails without the need for managing additional infrastructure.

While Amazon Simple Notification Service (SNS) can be used to send notifications, it is not designed specifically for email delivery. SNS is more suitable for pub/sub messaging patterns and lacks the features specifically tailored for email delivery that SES provides.

Creating a separate application tier using EC2 instances dedicated to email processing and placing them in an Auto Scaling group adds unnecessary complexity and operational overhead. It does not align with the goal of minimizing email delivery issues and operational efforts.