If you want to manually check if e-mail delivery works on a machine by sending an e-mail you can run the following:
mail -s Test someone@example.com < /dev/null

UI/UX Design by

We make sure that your target audience has the best possible experience with your digital product. You get:

• Design tailored to your audience
• Proven processes customized to your needs
• An expert team of experienced designers

Read more Show archive.org snapshot

This will send an empty e-mail with "Test" as its subject to someone@example.com.

If you want it to contain a message body, call mail -s Test someone@example.com only; the mail application will then read your input from stdin. Finish your message by sending EOT Show archive.org snapshot with Ctrl-D -- if you are asked for anything else (like CC addresses) you may press Ctrl-D again.