TYPO3 form with dynamic recipients

dynamicRecipients.form.yaml

identifier: formWithDynRecipients
label: 'Form with dynamic recipients'
type: Form
prototypeName: standard
renderingOptions:
  submitButtonLabel: Submit
finishers:
  -
    identifier: EmailToReceiver
    options: &emailToReceiverOptions
      subject: '{group} and {topic}'
      recipients:
        default@example.org: Default Recipient
      senderAddress: '{email}'
      senderName: '{name}'
      format: html
      attachUploads: true
      translation:
        language: default
      useFluidEmail: true
      title: 'Confirmation of your message'
  -
    identifier: Confirmation
    options: &confirmationOptions
      message: "Thanks for your message"
      contentElementUid: ''
renderables:
  -
    renderingOptions:
      previousButtonLabel: 'Previous Page'
      nextButtonLabel: 'Next Step'
    identifier: page-1
    label: ''
    type: Page
    renderables:
      -
        defaultValue: ''
        identifier: name
        label: 'Your name'
        type: Text
        properties:
          fluidAdditionalAttributes:
            placeholder: 'Your name'
            required: required
          elementDescription: ''
        validators:
          -
            identifier: NotEmpty
          -
            identifier: Alphanumeric
      -
        defaultValue: ''
        identifier: email
        label: 'Your Email'
        type: Text
        properties:
          fluidAdditionalAttributes:
            placeholder: 'Your email'
            required: required
          elementDescription: ''
        validators:
          -
            identifier: NotEmpty
          -
            identifier: EmailAddress
      -
        identifier: group
        type: SingleSelect
        label: 'group'
        properties:
          options:
            group1: 'Group 1'
            group2: 'Group 2'
            group3: 'Group 3'
          prependOptionLabel: '-- Please select --'
          fluidAdditionalAttributes:
            required: required
        validators:
          -
            identifier: NotEmpty
      -
        identifier: topic
        type: SingleSelect
        label: 'Topic'
        properties:
          options:
            topic1: 'Topic One'
            topic2: 'Topic Two'
          prependOptionLabel: '-- Please select --'
  -
    renderingOptions:
      previousButtonLabel: 'Previous Page'
      nextButtonLabel: 'Next Step'
    identifier: summarypage
    label: 'Summary page'
    type: SummaryPage
variants:
  -
    identifier: group1
    condition: 'formValues["group"] == "group1"'
    finishers:
      -
        identifier: EmailToReceiver
        options:
          <<: *emailToReceiverOptions
          recipients:
            group1@example.org: '{group}'
      -
        identifier: Confirmation
        options:
          <<: *confirmationOptions
  -
    identifier: group2_and_topic1
    condition: 'formValues["group"] == "group2" && formValues["topic"] == "topic1"'
    finishers:
      -
        identifier: EmailToReceiver
        options:
          <<: *emailToReceiverOptions
          recipients:
            group2-topic1@example.org: '{group} {topic}'
      -
        identifier: Confirmation
        options:
          <<: *confirmationOptions

ext_locallang.php

<?php

defined('TYPO3') || die('Access denied.');

(function () {
    \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTypoScriptSetup(
        trim('
             module.tx_form.settings.yamlConfigurations {
                 110 = EXT:my_extension/Configuration/Form/FormSetup.yaml
             }
             plugin.tx_form.settings.yamlConfigurations {
                 110 = EXT:my_extension/Configuration/Form/FormSetup.yaml
             }
        ')
    );
});

FormSetup.yaml

TYPO3:
  CMS:
    Form:
      prototypes:
        standard:
          formElementsDefinition:
            Form:
              renderingOptions:
                translation:
                  translationFiles:
                    20: EXT:my_extension/Resources/Private/Language/locallang_form.xlf

locallang_form.xlf

<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<xliff version="1.0">
  <file source-language="en" datatype="plaintext" original="messages" product-name="my_extension">
    <header/>
    <body>
      <trans-unit id="element.formWithDynRecipients.renderingOptions.submitButtonLabel">
        <source>Submit now</source>
      </trans-unit>
      <trans-unit id="formWithDynRecipients.element.page-1.properties.label">
        <source>Page one</source>
      </trans-unit>
      <trans-unit id="formWithDynRecipients.element.name.properties.label">
        <source>Your full name</source>
      </trans-unit>
    </body>
  </file>
</xliff>