Director is unable to send email alerts. The eventlogs has an event with Exception (0):

The data source 'Unknown error.' ('http://DDC.FQDN.COM/Citrix/Monitor/v1') responded with an unexpected error.

User: 'DomainName\UserName'

Console operation: 'Sending test message in mail...

Additional information:

'ExceptionThrown (0)'

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Director do not send emails directly from SMTP server, it contacts Delivery Controller to send emails. Add Delivery Controller server IP Address to the field "Receive mail from remote server that have this IP Address".

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Problem Cause

In the director logs, that exception is coming because service was unavailable:

MonitoringSdkServiceConnector exception string: System.Net.Mail.SmtpException: Service not available, closing transmission channel. The server response was: 4.3.2 Service not available 

The data source 'Unknown error.' ('http://DDC.FQDN.COM/Citrix/Monitor/v1') responded with an unexpected error.

Send-MailMessage returns The server response was: 4.3.2 Service not available