Allow AWS SES sourceArn to be set

part of #4173

Allows mail to be sent via AWS SES with a authorised identity

Author: hardillb

docs/install/configuration.md

@@ -140,6 +140,7 @@ This assumes that the instance is running with a Service Account that has a AWS
 Option        | Description
 --------------|------------
 `email.ses.region` | The AWS region to connect to
+`email.ses.sourceArn` | The AWS ARN of a Identity to send email as
 
 
 ## Telemetry configuration

forge/postoffice/index.js

@@ -81,6 +81,12 @@ module.exports = fp(async function (app, _opts) {
                     defaultProvider
                 })
 
+                if (sesConfig.sourceArn) {
+                    mailDefaults['ses'] = {
+                        sourceArn: sesConfig.sourceArn
+                    }
+                }
+
                 mailTransport = nodemailer.createTransport({
                     SES: { ses, aws }
                 }, mailDefaults)