SYMPTOM:
On executing a particular email service on the Strategy Narrowcast Server 9.x Administrator console, the email was not received by the end users defined in the service. But the email file output is generated as the following options was enabled in the Email Transmitter:

The end users are able to receive emails delivered by other Strategy Narrowcast Server 9.x services. The SMTP logs were being enabled as instructed in the following Strategy Knoweldge Base article:
KB9762: How to generate the Strategy SMTP Protocol log file for Strategy Narrowcast Server
The following message was found in the SMTP logs:
From the SMTP log, the email was being sent to the SMTP server, but the SMTP server did not deliver it to the recipient.
CAUSE:
One of the possible cause is that the file attached in the email is larger than the limit set on the Email Server.
ACTION:
There are three solutions to the problem caused by the file size: