"I assume UNA's default mailer is PHP mail?" YES

As email volume and requirements grow, UNA CMS can scale by using one of the following approaches:

1. Built-in UNA CMS PHP mail service – suitable for testing, development, or low-volume traffic.
2. External mail server – the CMS connects via authenticated SMTP to a reliable mail server for medium-volume traffic.
3. Dedicated SMTP service from a provider – for high-volume or critical emails, a scalable SMTP service ensures optimal deliverability, reputation management, and reliability.
4. Alternatively, if your organization has the expertise, it can build and manage its own SMTP infrastructure to fully control email delivery, scalability, and monitoring.

An SMTP server is straightforward to use, and its main advantage is that it connects directly to your email service. It works very well as long as it is installed and configured correctly. For critical or high-volume emails, an external SMTP server is safer and more efficient than sending directly from your CMS server, as almost any mail provider offers SMTP functionality. However, for true scalability, a dedicated SMTP service is required. The built-in mail service in UNA CMS is intended primarily for testing environments, development, or low-volume email traffic, as its capacity depends on the server’s infrastructure and resources you have.