Messages are sent correctly, but not received

Hi all,

I need a help.

I started sending test messages, and I made sure that they reach my personal mail, but when I sent a large number in one go, sending started fine, but after some time it stopped, But messages are still waiting, now more than 24 hours have passed but not sent.

How do I solve this problem?

Information : Provider : vps in hostinger Operating system Ubuntu Linux 20.04.2 Webmin version 1.973 Usermin version 1.823 Virtualmin version 6.16
Authentic theme version 19.73 Kernel and CPU Linux 5.4.0 on x86_64

Help me please.

Closed (won't fix)
Virtualmin version: 
Webmin version: