You can only send to & X.400 addresses

What causes this issue?

The maximum number of recipients allowed per send operation was
exceeded. This number is defined in the SAP user master.

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?

Check your Office user to see how many recipients you can address. To
send the document to all recipients, carry out several send operations.

Error message extract from SAP system. Copyright SAP SE.