Note: it is not recommend by SAP to manually change system table fields value but besides use Diapi or Service layer to resend those emails, this is the only way to do that for customers.
For some reason, SMTP server could reject those Email you sent by using SBO Mail service. Those Email will be saved in sent queue but with the status "Error". If Cusotmer want you to resend them when the SMTP server back to normal, here's the method.
update ALR1 set Status = 'U' where Code = '9257' ALR1 is the queue of messages to be sent table (OALR is the message detail information table)
update OAOB set WasSent = 'N' where AlertCode = '9257' Both OAOB and AOB1 are message sent tables
update AOB1 set Confirmed2 = 'N' where AlertCode = '9257'
update AOB1 set ConfDate2 = null where AlertCode = '9257'
update AOB1 set ConfTime2 = null where AlertCode = '9257'
All those Messages will have a Code or AlertCode in database, please check it to match your record in B1 with AOB1 or ALR1 table.
You dont have to restart the SBO Mail server. The SBO Mail server will check those fields when the time is up and send those Emails in the queue again.
To check if the Email is resend or not, use the following query
select * from AOB1 where AlertCode = '9257'
If "Confirmed2" = 'Y', the Email is successful sent. If "E", please check SBO Mailer server - event viewer - Windows Logs - Application for troubleshooting.