Problem with sending alerts to email

Hello,
Maybe someone had a similar problem.
I have two librenms environments not clustered, on two completely different networks.
And on both of these servers there is a problem with sending alerts , just emails do not go out, in tcpudmp to the mail server address you do not see any packets being sent.
The problem occurs once in a while, and I do not know if there may be a problem.
Test mail goes out always.