Mails not sent

FAQ > I see a response message “Thank you for your message. It has been sent.” with green border, but I never receive a mail for that.

Hello, thanks for your answer, but no, it is not that. It DELIVERS the mail only to the first address in the row, a yahoo mail address. The other 2 addresses does not receive the mail – a gmail one and the last one is associated with the domain.

I have also tried the CC and BCC in header, but still nothing. Not in spam, not anywhere.