Add ADR for using SES to send confirmation emails

ADR/ADR050-use-ses-to-send-confirmation-emails.md

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+# ADR050: Use Amazon SES to send confirmation emails
+
+Date: 2026-05-13
+
+## Status
+
+Accepted
+
+## Context
+
+We currently use GOV.UK Notify to send confirmation emails to form fillers when they submit a form. We already use
+Amazon SES to send submission emails to processing teams. We previously used Notify for sending submission emails, but
+switched to using SES as we needed to be able to attach files to emails - see [ADR019: Use Amazon
+SES](ADR019-use-amazon-ses.md). An additional benefit was SES gave us more control over the formatting of emails, which
+allowed us to improve how we display the answers.
+
+We are adding a feature to allow form fillers to receive a copy of their answers in the confirmation email. We want to
+use the same formatting for the answers in both submission and confirmation emails rather than having to maintain two
+different formats for SES and Notify.
+
+## Decision
+
+We will use Amazon SES to send confirmation emails to form fillers when they submit a form, instead of GOV.UK Notify.
+
+Initially, this will just be when they opt to receive a copy of their answers, but we should also make this change for
+confirmation emails that don't include the answers in the future for consistency.
+
+We will continue to use GOV.UK Notify for sending emails to admin users.
+
+## Consequences
+
+Pros:
+- We only need to maintain one format for the answers in the emails, rather than needing to support separate formatting
+  for use in Notify.
+- We will be able to attach uploaded files to confirmation emails if we want to in the future.
+- We are only reliant on one email provider for the form filler journey, which should be easier to maintain.
+
+Cons:
+- We will no longer be able to use the Notify interface to check whether emails were successfully sent. However, we have
+not used this often for support.
+- We will need to handle bounces and complaints for confirmation emails in SES. We shouldn't need to take any action on
+  these, but we will need to ensure our reputation as a sender isn't negatively impacted.