Customers registering at some of my client sites are not receiving the confirmation email.

I believe I have it set up correctly because the test email in Joomla Global Configuration works, AcyMailing works, and DT Register works. I've also checked to be sure I have email set up correctly in cPanel.

I tried a different site this morning and it sent an email, but it took almost an hour to be received. The Joomla, AcyMailing and DT Register emails all came in almost instantly.

Is there something obvious I missed in setting up CB on this site?

Thank you,
Ernie

I tried Mass Mailer and it failed:

Error sending email: SMTP connect() failed. github.com/PHPMailer/PHPMailer/wiki/Troubleshooting

I'm using SMTP with the customer's domain email address.

Oddly, I have several other sites set up with SMTP. I tested one, and it quickly sent the email to me.

I changed to PHP Mail and it worked.

But for future reference, what might be the reason SMTP didn't work for this site but worked for the other site?

Thank you,
Ernie