Hi Piyush,
For Error 1: check system property messaging.backoffintervalmins. It should have a number value.
For Error 2: you are connecting to the SMTP with userA@abc.com (from system prop) and trying to send an email 'from' userB@abc.com (email from address) ... The SMTP server doesn't allow that.
From this error it looks like your Sourcing system is actually connecting to the SMTP server. I'm puzzled as to why your email team said they are not receiving any connections.
Bogdan