SMTP Outbound Connection Test Validation Failed with Error "Test was not successful: Email test error: [535 5.7.8 Error: authentication failed: authentication failure ]"

Products

• VCF Operations/Automation (formerly VMware Aria Suite)

Issue/Introduction

• SMTP Outbound Connection Test Validation Fails with Error "Test was not successful: Email test error: [535 5.7.8 Error: authentication failed: authentication failure ]"
  
• Trying with different email account gives the same error.
• The same account works fine when logging into email client.
• The analytics logs displays below events:

  analytics-.log:2025-10-08T08:01:06,104+0000 ERROR [ServerConnection on port 10000 Thread 4710]  com.vmware.vcops.plugins.filter.EmailPlugin.test - Email test failed: [Could not connect to SMTP host: mail.domain.co, port: 587] 
  analytics-.log:2025-10-08T08:01:12,904+0000 ERROR [ServerConnection on port 10000 Thread 4710]  com.vmware.vcops.plugins.filter.EmailPlugin.test - Email test failed: [Could not connect to SMTP host: mail.domain.co, port: 587] 
  analytics.log:2025-10-08T08:01:15,577+0000 ERROR [ServerConnection on port 10000 Thread 4710]  com.vmware.vcops.plugins.filter.EmailPlugin.test - Email test failed: [Could not connect to SMTP host: mail.domain.co, port: 587]

• We are able to connect via Openssl Command:

  openssl s_client -connect mail.domain.co:587 -starttls smtp

• Running the below command fails to connects to the SMTP server with 'Error: authentication failed: authentication failure|Login denied'

  curl --url "smtp://mail.domain.co:587" --ssl-reqd --user '[email protected]:Password' --mail-from "[email protected]" --mail-rcpt "[email protected]" --verbose  

Environment

Aria Operations 8.17.X and Later

Cause

• The authentication failures is seen on the mail server due to the following reasons:

  • Rate limiting or temporary lockout of the sender account

  • IP-based throttling or authentication caching

  • Load balancing across multiple mail nodes, where one backend node intermittently fails authentication

Resolution

• Reach out to the SMTP provider to identify and resolve the issue.