We have been using ZOHO SMTP server for sending out email. But suddenly it stopped working today. There was no mailbox blockage, nor mailbox is full. Below the error log we're getting. What could potentially be the causes of this?

javax.mail.MessagingException: Could not connect to SMTP host: smtp.zoho.com, port: 465;
nested exception is:

javax.mail.MessagingException: Could not connect to SMTP host: smtp.zoho.com, port: 465;
nested exception is:
java.net.ConnectException: Connection timed out (Connection timed out)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1282)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:370)
at javax.mail.Service.connect(Service.java:275)
at javax.mail.Service.connect(Service.java:156)
at com.hftsolution.util.MailController.sendMail(MailController.java:110)
at com.hftsolution.camel.service.CustomerRegistration.lambda$0(CustomerRegistration.java:79)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.net.ConnectException: Connection timed out (Connection timed out)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:232)
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:189)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1250)