Some email providers (like Hotmail) may not allow these emails (sent by server's mail() function) to be delivered. Please try to use different email address in your website settings (like Gmail) or use SMTP setup, it's also available in your website's configuration: you enter your username/password to your mailbox and all messages are sent the same way as you would send them from your computer or phone.

• Step #1
  SMTP setup for sending emails
  In left toolbar, go to SETTINGS section and there General Settings.
• Step #2
  Find "Administrator's e-mail" section and click "more settings" link there, a new window will appear: "Method for sending emails", choose "SMTP" option there and setting form will appear.
• Step #3
  For the Email settings you'll need to enter your mailbox details here: email address and password, but also "port" (usually 587 or 465, but if none of these work, ask your webhosting company for assistance) and hostname, usually it's your email's domain name - if your email is my-email@company.com, hostname will be company.com or smtp.company.com or something similar.

Example
If you use Google's Gmail, your email address is john@gmail.com and password is "12345", in SMTP settings you set smtp.gmail.com as hostname, 465 as port your email address is SMTP Username and your password in SMTP Password

• Step #4
  Make a test
  When form is filled, click "verify" button to make sure system can send emails. It'll show "save" button - click there to save changes and to make sure everything works well, use contact form to send test message.
• Step #5
  Google App Passwords
  If you're setting up Google's Gmail in your SMTP, it's possible your account is set to use "app passwords", separate password for each app, you may need to check this page and generate a separate password for your website's SMTP settings.