Mails sent successfully but not received neither in inbox, promotion and spam folder

Hi everyone,

I have recently built my SMTP server on webmin postfix mail server and I was sending emails everything was working fine. I am using Mautic application, and I have connected it to my SMTP server. So yesterday I sent emails from my mautic application to two of my Gmail accounts. In the Mautic application it shows that the message was sent but when I checked my Gmail inbox, promotion, spam folder there was no message received. Then I opened my postfix mail server queue section to see whether the emails are stuck there but no there was no emails in queue section and even I have not received any error message of failed delivery.So where the message went. This is a big problem because I have been sending emails to my list and all of the emails were shown sent but maybe they are never received to my customers.

I see that the open rate is less than 1%, but I was ignoring this because my SMTP server is new. May be any of my customers didn’t received my emails. All of the records Dmarc, SPF, PTR, DKIM are setup properly. Even I got 10/10 score when I tested my emails on