Sending mail to external mail address

Hello Everyone,

I am facing a problem in sending mail to external mail address using the SENDMAIL step in workflow. I created a simple workflow which has only SENDMAIL step using a container element which has the email address in the initial value.

When I execute the workflow, it is going into error status. On going through the workflow log the message which is being displayed in technical log is

"Executing batch item -

Work item 000000437150: Object 000000437150 method SENDTASKDESCRIPTION cannot be executed.

Executing Batch work item - Document could not be sent"

When I try manually to send a message from SBWP to other mail address,it is working fine. Please let me know where the error could be?

Regards,

Samson