Log file is mention below :
2015-09-02 12:30:57,748 WARN [sync-mbox-dknishad@hpclbiofuels.co.in] [] smtp - Unable to connect to SMTP server: java.net.ConnectException: Connection timed out: connect.
2015-09-02 12:30:57,748 ERROR [sync-mbox-dknishad@hpclbiofuels.co.in] [] offline - exception encountered during sync
com.zimbra.cs.mailbox.MailServiceException: try again: Unable to connect to the MTA
ExceptionId:sync-mbox-dknishad@hpclbiofuels.co.in:1441177257748:9426f78eba184a09
Code:mail.TRY_AGAIN
at com.zimbra.cs.mailbox.MailServiceException.TRY_AGAIN(MailServiceException.java:484)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(MailSender.java:628)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(MailSender.java:425)
at com.zimbra.cs.mailbox.DataSourceMailbox.sendPendingMessages(DataSourceMailbox.java:314)
at com.zimbra.cs.mailbox.DataSourceMailbox.sync(DataSourceMailbox.java:477)
at com.zimbra.cs.mailbox.DataSourceMailbox.syncOnTimer(DataSourceMailbox.java:406)
at com.zimbra.cs.mailbox.SyncMailbox$1.run(SyncMailbox.java:279)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(Unknown Source)
at java.net.PlainSocketImpl.connectToAddress(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:317)
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:207)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1938)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:642)
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:146)
at com.zimbra.cs.mailbox.MailSender.sendMessage(MailSender.java:833)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(MailSender.java:565)
... 7 more