CloudLink：CloudLinkメール通知が機能しない「Sending the email to the following server failed...」

2023-02-20 04:39:17,377 ERROR [/cloudlink/rest/email/test (qtp1485955886-192095)] c.a.g.e.s.m.EmailNotificationServiceBean.sendTestEmail(…) (EmailNotificationServiceBean.java:179) Failed to send test email: Sending the email to the following server failed: xxxxx.xxxxx.com.xxx:25
org.apache.commons.mail.EmailException: Sending the email to the following server failed: xxxxx.xxxxx.com.xxx:25
    at org.apache.commons.mail.Email.sendMimeMessage(Email.java:1469)
    at org.apache.commons.mail.Email.send(Email.java:1496)
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Caused by: javax.mail.MessagingException: Could not connect to SMTP host: mailout.optus.com.xxxxx.xxxxx.com.xxx, port: 25, response: 554
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2106)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:712)
    at javax.mail.Service.connect(Service.java:295)
    at javax.mail.Service.connect(Service.java:176)
    at javax.mail.Service.connect(Service.java:125)
    at javax.mail.Transport.send0(Transport.java:194)
    at javax.mail.Transport.send(Transport.java:124)
    at org.apache.commons.mail.Email.sendMimeMessage(Email.java:1459)
    ... 95 common frames omitted