My verification emails to customers are not being received Is sending to Canada an issue

One of my customer in canada has yet to receive email verifictaion. I sent several times and to two separate email addresses. He is in Canada, if that makes a difference.

Hey there!

I know it sounds boring but I need to ask you a couple of email troubleshooting questions:

  1. Have they checked SPAM?
  2. What email provider you use for sending out those emails?
  3. What email clients those people use that do not receive these emails?

Yes, they checked SPAM. And we sent to a gmail account from our gmail account.