Distribution list contains an inconsistent entry

What causes this issue?

The distribution list contained one or more entries which were no
longer valid.

System Response

Incorrect entries were removed from the display list.

How to fix this error?

Save the distribution list in order to store the list in the corrected
form.
If you cannot save the distribution list yourself, contact someone with
maintenance authorization for this distribution list.
Apart from this, you can ignore this message.

Error message extract from SAP system. Copyright SAP SE.