Office function module showed return code '&'.

What causes this issue?

The office function module provided the return code &v1&.
As a result, the IDoc could not be sent as an Internet mail.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Please inform your system administrator.

Error message extract from SAP system. Copyright SAP SE.