Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

1. Install Jira Server on any version from 9.2.0
2. Log into Jira as a Jira System Admin user
3. Go to ⚙ > System > Outgoing Mail
4. Configure a the SMTP Mail Server without specifying the combo username/password
5. Click on the button Test Connection

Expected Results

The connection test should be successful.

Actual Results

The below exception is thrown when testing the connection.

AuthenticationFailedException: 535 5.7.0 authentication failed 

If we enable DEBUG for Outgoing Mail and check the Jira Outgoing Mail Logs, we can see that Jira sends user name when not specified (this can vary depending on instance setup):

/secure/admin/VerifySmtpServerConnection!add.jspa [c.atlassian.mail.outgoing] DEBUG SMTP: protocolConnect login, host={smtp}, user=jira, password=<non-null> 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available