Transaction SOST is used to check if there are any failed e-mails or faxes that did not go out from SAP. By default the Period will be the current day plus the previous and the Sent Status will include Waiting, Errors, and Sent.
The main item of concern is Errors. When you encounter an error please review and if possible attempt to resend. Selecting the failed item and selecting Repeat Send will attempt to resend the message.
