I did checked by many ways and I guess it’s plugin problem with the latest 6.5.8 though my issue has not been shut-out yet. I m still seeking for an solution. Below are some of the solution I tried as per my hosting company as far as i know but none of them worked.
1. Changed PHP and WordPress version.
2. Reset configuration and tested other emails by creating it.
3. Re install 6.5.7 ver. of plugin and updated as well.
4. Tested on PHPMailer and works there but not with plugin out here.
Is any one facing same issue here. Please let me know if you have any solution.