Transport connection has been closed

Good day all

We are having some difficulties lately with the Workflow Mailer. We have the following message in the logs: Transport connection has been closed.

Anyone have any idea why the connection close all the time?

[Apr 28, 2021 4:54:21 AM EDT]:1619600061499:-1:-1:oraung01.iamgold.com:10.10.4.90:-1:-1:1:20420:SYSADMIN(0):-1:Thread[JavaMail-EventQueue,5,outboundThreadGroup]:1959599047:80813:1619599101979:53:STATEMENT:[SVC-GSM-IMG_EAM_WF_MAIL_SVC-6278527-11000 : oracle.apps.fnd.wf.mailer.SMTPMessageHandler$TransportMonitor.closed(ConnectionEvent)]:Transport connection has been closed
[Apr 28, 2021 4:54:21 AM EDT]:1619600061499:-1:-1:oraung01.iamgold.com:10.10.4.90:-1:-1:1:20420:SYSADMIN(0):-1:Thread[outboundThreadGroup1,5,outboundThreadGroup]:1959599047:80813:1619599100877:52:STATEMENT:[SVC-GSM-IMG_EAM_WF_MAIL_SVC-6278527-11000 : oracle.apps.fnd.wf.mailer.SMTPMessageHandler.sendMessages(String)]:Call back event {null}
[Apr 28, 2021 4:54:21 AM EDT]:1619600061499:-1:-1:oraung01.iamgold.com:10.10.4.90:-1:-1:1:20420:SYSADMIN(0):-1:Thread[outboundThreadGroup1,5,outboundThreadGroup]:1959599047:80813:1619599100877:52:UNEXPECTED:[SVC-GSM-IMG_EAM_WF_MAIL_SVC-6278527-11000 : oracle.apps.fnd.cp.gsc.Processor.run()]:java.lang.IllegalStateException: Not connected
	at com.sun.mail.smtp.SMTPTransport.checkConnected(SMTPTransport.java:2355)
	at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1151)
	at oracle.apps.fnd.wf.mailer.SMTPMessageHandler.send(SMTPMessageHandler.java:968)
	at oracle.apps.fnd.wf.mailer.SMTPMessageHandler.sendMessages(SMTPMessageHandler.java:427)
	at oracle.apps.fnd.wf.mailer.SMTPMessageHandler.processMessage(SMTPMessageHandler.java:1645)
	at oracle.apps.fnd.cp.gsc.SvcComponentProcessor.process(SvcComponentProcessor.java:659)
	at oracle.apps.fnd.cp.gsc.Processor.run(Processor.java:283)
	at java.lang.Thread.run(Thread.java:745)