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Editorial Team
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Asked: 2026-06-12T04:58:08+00:00

we are configuring email server in our application with own mail server but while

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we are configuring email server in our application with own mail server but while sending mail i got this exception.

  host = "mail.xxx.com"
  port = 25
  username = "xx@xx.com"
  password = "xx"
  props = ["mail.smtp.auth":"true",
            "mail.smtp.socketFactory.port":"25",
            "mail.smtp.socketFactory.class":"javax.net.ssl.SSLSocketFactory",
            "mail.smtp.socketFactory.fallback":"false"]

 org.springframework.mail.MailSendException: Mail server connection failed; nested exception is javax.mail.MessagingException: Could not connect to SMTP host: mail.co-optimum.com, port: 25;
  nested exception is:
    javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?. Failed messages: javax.mail.MessagingException: Could not connect to SMTP host: mail.co-optimum.com, port: 25;
  nested exception is:
    javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?; message exceptions (1) are:
Failed message 1: javax.mail.MessagingException: Could not connect to SMTP host: mail.co-optimum.com, port: 25;
  nested exception is:
    javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection

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1 Answer

  1. Editorial Team

    The top three reasons that i’ve seen this happen is due to the following:

    1. The TCP port is blocked on the application server due to security policy
    2. The TCP port is blocked by firewall or other network device due to security policy
    3. The target SMTP server requires you to “whitelist” your application server to allow the connection.

    All three cases happens because a company wants to prevent spammers from using their email server has spam delivery systems.

    Talk with your support personnel.

    hope that helps…

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