Vivian Mail

Vivian Mail is a tiny and easy-to-use email client that enables you to seamlessly manage your messages from multiple accounts gathered in a single place. It contains some basic options that can swiftly figured out.
Before proceeding any further, you should know that the tool hasn't been updated for a long time, so it likely has compatibility issues on later Windows editions.

Set up multiple email accounts

You can get started by setting up a new email account using a simple wizard with a classical look, which requires your screen name, email address, POP3 and SMTP server address, POP3 user account and password, along with an account name.
It's possible to add as many accounts as you want, edit their properties, and remove them from the manager in just a couple of clicks.

Manage emails and contacts easily

Vivian Mail loads the inbox, outbox, template, sent and trash folders. You can compose a new email and send it to multiple recipients from any preferred account, attach signatures and files, as well as view the message source in a plain text document.
The software application also lets you forward or redirect messages, manage an address book with contacts, print information, use a basic search function, enable word wrapping mode, show the cc and bcc header fields, create message filters, or add the current sender to the address book.

Evaluation and conclusion

Although it hasn't been updated for a very long time and it's now a discontinued project, the tool is still functional. As expected, it left a small footprint on system resources, using low CPU and RAM.
To conclude, it may not be feature-rich, but its options are practical and intuitive, so you can test Vivian Mail for yourself if you're looking for a straightforward email client with uncomplicated configuration settings.