JavaMail Issue : Can't send command to SMTP host

Question

I\'m trying to do java mail and im getting an error \"Cant send command to SMTP host\". Any help would be appreciated. And any future problems\' solutions if possible. The e

Answer 1

In my case, I was able to find the root problem after I enabled mailer debugging.

Different ways to enable mailer debugging:

java -Dmail.debug=true ...

props.put("mail.smtp.starttls.enable", "true");
props.put("mail.debug", "true");

Jenkins config (/etc/default/jenkins):

JAVA_ARGS="-Dmail.smtp.starttls.enable=true -Dmail.debug=true"

More info: http://www.oracle.com/technetwork/java/faq-135477.html

My particular error was that I had an incorrect address in the "from:" line when the email was created. Google "G Suite" (google apps for business) requires the from-address to be in the same domain as the account owner. Eg. mycompanyname.com

The mailer debug revealed:

MAIL FROM: 550-5.7.1 Invalid credentials for relay [192.168.42.42]. The IP address you've 550-5.7.1 registered in your G Suite SMTP Relay service doesn't match domain of 550-5.7.1 the account this email is being sent from. If you are trying to relay 550-5.7.1 mail from a domain that isn't registered under your G Suite account