Update diagrams/sequence-diagrams/sending-submission-emails.md

Co-authored-by: Stephen Daly <stephen.daly@digital.cabinet-office.gov.uk>

Author: lfdebrux

diagrams/sequence-diagrams/sending-submission-emails.md

@@ -76,7 +76,7 @@ end
 
 ses->>worker: return message_id
 worker->>runner-db: set mail_message_id on Submission
-worker->>runner-db: update mail_status of Submission to "pending"
+worker->>runner-db: set the last_delivery_attempt timestamp on Submission
 
 ses-)inbox: send email
 note over ses,inbox: happens some time later