SMTP configuration requests authentication but should allow anonymous

Attempting to setup mail server on Stash.

Sending test email returns error requesting authentication, however exchange server allows anonymous (as used by other tools such as Jenkins).

Log file from: atlassian-stash-mail.log

subject: Stash - Test email for your SMTP configuration
org.springframework.mail.MailSendException: Failed messages: com.sun.mail.smtp.SMTPSendFailedException: 530 5.7.1 Client was not authenticated

at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:440) ~[spring-context-support-3.2.2.RELEASE.jar:3.2.2.RELEASE]

I executed on my Oracle DB:
SELECT * FROM app_property WHERE prop_key LIKE 'mail.%';

and it returned only:
mail.host
mail.sender.address
mail.useTLS

Everytime I clean the username/password fields on the "Mail server configuration" screen and click on "Save", those credentials come back.

Please advise.

Thanks
Jonny