I believe this is a relaying issue. Your mail server does not allow you to send emails to the "rurex.com.pl" domain. Check the mail server configuration.
Rob Prime wrote:At least your program has made some progress
I believe this is a relaying issue. Your mail server does not allow you to send emails to the "rurex.com.pl" domain. Check the mail server configuration.
This code doesn't allow to send the emails as for all 20,000 emails same error
I'm not familiar enough with your mail server program (or any other mail server program, to be honest) to answer that question. I don't think you can get much help here if it's not caused by Java code. Try the site of the mail server program itself.