Hello @bomit
Good Day.
We are glad that the initial issue got resolved.
As far as this issue is concerned
Communication Error [334] – make sure the Envelope From email is the same account used to create the Client ID
We would suggest you to use the same email as From Email that you used to configure Post SMTP. Additionally, you could follow these steps and the issue will hopefully be resolved:
Go to Post SMTP -> Settings -> Message -> Email Address & Check on “Prevent plugins and themes from changing this” box. See Screen Shot for reference.
Moreover, share your Diagnostic Test report & the Socket that you are using so that we could further assist you.
We are delighted that you are not seeing any error messages for now. If you have any concern feel free to open new thread with us.
Thanks and regards,
Support Team – WP Experts