@Nabeel I'm having the same issue. According to the log file, seems like the SMTP Greeting is returning nothing instead of the expected 220. Was using the forgot password function so got a full error screen and was able to export it to Flare so here's the full error information including stack trace, request details etc
https://flareapp.io/share/4m41E4PM#F59
Tried adding mail details to env.php file, config/mail.php and config.php but to no avail.