If you have sent a message via e-mail that the recipient did not receive, it may be due to:

• The email address is misspelled
  Check the customer’s email address on their profile.

• The person lacks consent to mass sending of email
  Make sure the person has consented to mass sending of email. You can see this on the person's profile, at the bottom of the "Person" tab.

• The email has ended up in the recipient's spam folder
  Ask the person to check their spam folder

If you have checked the points above, ask the customer to add your email address as a contact and then try to send the email again.