My entire organization is experiencing an issue where email delivery times are significantly delayed

[azizihazim]

Hi,
my whole organisation has same isue their email sending taking to long to receive. 
and some of their email get rejected.
here one of the error when i check..

btw im working for university, I'm still pretty new here , only been here for 10 months. and i need to take care gws admin portal for my university. i have around 10k user rn.

Has anyone in a similar situation get solve this problem? If so, how?

Thank you,

Azizi