Very often, such mail arrives ages later in a bulk. Have you also checked the spam folder?
Are you on a Mac? Then you can try to log what is happening like I suggested here: Kirby Mail - Sending to multiple recipients
However, I suggest you install MailHog or a similar software locally for testing. It has the additional advantage that your IP doesn’t get blocked for sending Spam.
Instead of sending through your own server, you could also try with a mail service.