Minutes / Hours DELAY IN ALL OUTGOING MAIL

Minutes / Hours DELAY IN ALL OUTGOING MAIL

All my outgoing mail has been lagging by minutes / hours (randomly) or sometime 12-14 hours delay.
and i can receive some email as normal (receive 1-2 minute after the script sent email)

It's not very certain. When will there be a problem.
Some days there are intermittent problems.​

I use the same script for sending email (no problem for a year until i get this issue again),
so i don't think it is the script problem.
It happen to every user email.

It happen for 7-8 days now and ZOHO support cannot fix this problem.

Anyone get the same problems??? and how to solve this???