3015176 - SMTP Email Alerts are not sent because of Communication Error

Email Notifications are not sent for scheduled tasks on XS Classic Applications or from HANA SDI Tasks and the following error is observed

Error: error couldn't establish connection 

The HANA XS Engine trace file shows

e XSMail           SMTPConnection.cpp(00290) : Connect to host '<host_name>:25' failed!
e JavaScript       Mail.cpp(00763) : Couldn't send mail: exception  1: no.2530005  (XSEngine/Connectivity/Smtp/SMTPConnection.cpp:291)
    error coulnd't establish connection
exception throw location:
 1: 0x00007fe540e61774 in xsengine::SMTPConnection::open()+0x720 at XSSmtpExceptions.h:28 (libhdbxsapi.so)
 2: 0x00007fe540e61a48 in xsengine::SMTPConnection::sendMail(xsengine::Mail&)+0x144 at SMTPConnection.cpp:110 (libhdbxsapi.so)
 3: 0x00007fe54048c150 in jsvm::MailObject::MailWrapper_send(JSContext*, unsigned int, JS::Value*)+0x2b0 at DiagTopic.hpp:383 (libhdbjsjm.so)
 4: 0x00007fe5409a5396 in js::Invoke(JSContext*, JS::CallArgs const&, js::MaybeConstruct)+0x192 at jscntxtinlines.h:240 (libhdbjsjm.so)

SAP HANA 1.0 and 2.0

SMTP, XSMail, Email Alert, SDI, hdbreptask, failure, alert , KBA , HAN-AS-XS , SAP HANA Extended Application Services , HAN-DP-SDI , SAP HANA smart data integration (SDI) , Problem