SAP Message WL686 - Info mail & could not be sent to recipient &

Diagnosis
There are inquiry mails for the work item without replies. When thework item is processed, these recipients are informed. To do this, aninformation mail is sent which can be used to delete the first mail.The mail informs the recipient that he does not need to process theinquiry mail since the work item has already been processed.

System Response
The mail <(>&<)> could not be sent to user <(>&<)> due to errors whichoccurred during sending.