All emails are correctly set, all green marked + PTR sent to big email provider.
AApanel = email A
Other email server = email B
email A -> sent first email -> not received (no error)
email A -> sent second email after 2 mins -> received
email B -> sent first email to email B -> not received
email B -> sent second email -> received
email B-> sent 2 emails to 2 emails on different domains in same VPS aapanel -> 1 received, the second not
email B -> sent 2 emails to 2 emails on different domains in same VPS aapanel -> both received
and SOMETIMES:
i sent 2 emails from email B to email A, i received second email, then after 10 minutes the first email delivered.
This happened only few times and its really hard to check if the other part received or not. How to fix this problem?
