Message SAP XS754 - Sender specification is initial or syntactically incorrect

Diagnosis
The specified sender address &V1& of type "&V2&" is initial or invalid.

System Response
This email or fax is delivered but replies or particular status messages(e.g. confirmation that the message has been read) are not possible.
Additional information on the node used (if available, in the systemlanguage for the node):
V4
Error number if available:
V3

Procedure
You should inform the manufacturer of the relevant communication systemof the error. The sender information should be delivered to the SAPsystem with the correct syntax.