Email notification not triggering to external candidates after 24A upgrade

Hi Experts,

 We have an issue with lower instance after upgrading to 24A, emails are not triggering to external candidates like while applying verification code email, job application confirmation email, identity confirmation email etc. But from backend in report we could see email triggered from ORC but its not reaching to candidate personal emails like gmail,Hotmail,outlook etc. I have raised the SR from 2 weeks we are not getting any solution still operation is working on it. Its impacting our new release testing also we are afraid that in production also if we get this kind of issue after upgrad!