can not connect outgoing mail

[ducna96]

in this host install jira, i telnet was successful to mail server with port 25
i dont know why container cannot connect to mail server with port 25
just i can ping from container to host.
i use iptables ,may be by iptables ?
please help me :((
com.atlassian.mail.MailException: com.sun.mail.util.MailConnectException: Couldn't connect to host, port: mail.tiin.vn, 25; timeout 10000;
nested exception is:
java.net.UnknownHostException: mail.tiin.vn
at com.atlassian.mail.server.impl.SMTPMailServerImpl.sendWithMessageId(SMTPMailServerImpl.java:222) [atlassian-mail-5.0.0.jar:?]
at com.atlassian.mail.queue.SingleMailQueueItem.send(SingleMailQueueItem.java:44) [atlassian-mail-5.0.0.jar:?]
at com.atlassian.mail.queue.MailQueueImpl.sendBufferUnderLock(MailQueueImpl.java:103) [atlassian-mail-5.0.0.jar:?]
at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:56) [atlassian-mail-5.0.0.jar:?]
at com.atlassian.jira.mail.JiraMailQueue$1.apply(JiraMailQueue.java:51) [classes/:?]
at com.atlassian.jira.mail.JiraMailQueue$1.apply(JiraMailQueue.java:48) [classes/:?]
at com.atlassian.jira.util.velocity.DefaultVelocityRequestContextFactory.runWithStaticBaseUrl(DefaultVelocityRequestContextFactory.java:110) [classes/:?]
at com.atlassian.jira.util.DefaultBaseUrl.runWithStaticBaseUrl(DefaultBaseUrl.java:50) [classes/:?]
at com.atlassian.jira.mail.JiraMailQueue.sendBuffer(JiraMailQueue.java:48) [classes/:?]
at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueService.java:21) [classes/:?]
at com.atlassian.jira.service.JiraServiceContainerImpl.run(JiraServiceContainerImpl.java:68) [classes/:?]
at com.atlassian.jira.service.ServiceRunner.runService(ServiceRunner.java:62) [classes/:?]
at com.atlassian.jira.service.ServiceRunner.runServiceId(ServiceRunner.java:44) [classes/:?]
at com.atlassian.jira.service.ServiceRunner.runJob(ServiceRunner.java:32) [classes/:?]
at com.atlassian.scheduler.core.JobLauncher.runJob(JobLauncher.java:134) [atlassian-scheduler-core-3.0.0.jar:?]
at com.atlassian.scheduler.core.JobLauncher.launchAndBuildResponse(JobLauncher.java:106) [atlassian-scheduler-core-3.0.0.jar:?]
at com.atlassian.scheduler.core.JobLauncher.launch(JobLauncher.java:90) [atlassian-scheduler-core-3.0.0.jar:?]
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.launchJob(CaesiumSchedulerService.java:435) [atlassian-scheduler-caesium-3.0.0.jar:?]
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.executeLocalJob(CaesiumSchedulerService.java:402) [atlassian-scheduler-caesium-3.0.0.jar:?]
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.executeQueuedJob(CaesiumSchedulerService.java:380) [atlassian-scheduler-caesium-3.0.0.jar:?]
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService$$Lambda$1119.000000008AEADC10.accept(Unknown Source) [?:?]
at com.atlassian.scheduler.caesium.impl.SchedulerQueueWorker.executeJob(SchedulerQueueWorker.java:66) [atlassian-scheduler-caesium-3.0.0.jar:?]
at com.atlassian.scheduler.caesium.impl.SchedulerQueueWorker.executeNextJob(SchedulerQueueWorker.java:60) [atlassian-scheduler-caesium-3.0.0.jar:?]
at com.atlassian.scheduler.caesium.impl.SchedulerQueueWorker.run(SchedulerQueueWorker.java:35) [atlassian-scheduler-caesium-3.0.0.jar:?]
at java.lang.Thread.run(Thread.java:813) [?:1.8.0_212]
Caused by: com.sun.mail.util.MailConnectException: Couldn't connect to host, port: mail.tiin.vn, 25; timeout 10000;
nested exception is:
java.net.UnknownHostException: mail.tiin.vn
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2194) [javax.mail-1.6.0.jar:1.6.0]
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:726) [javax.mail-1.6.0.jar:1.6.0]
at javax.mail.Service.connect(Service.java:388) [javax.mail-1.6.0.jar:1.6.0]
at javax.mail.Service.connect(Service.java:246) [javax.mail-1.6.0.jar:1.6.0]
at javax.mail.Service.connect(Service.java:195) [javax.mail-1.6.0.jar:1.6.0]
at com.atlassian.mail.server.impl.SMTPMailServerImpl.sendWithMessageId(SMTPMailServerImpl.java:182) [atlassian-mail-5.0.0.jar:?]
... 24 more
Caused by: java.net.UnknownHostException: mail.tiin.vn
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184) [?:1.8.0_212]
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) [?:1.8.0_212]
at java.net.Socket.connect(Socket.java:589) [?:1.8.0_212]
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:350) [javax.mail-1.6.0.jar:1.6.0]
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:238) [javax.mail-1.6.0.jar:1.6.0]
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2160) [javax.mail-1.6.0.jar:1.6.0]
... 29 more