diff --git a/packages/backend/src/apps/postman/common/parameters.ts b/packages/backend/src/apps/postman/common/parameters.ts
index dbfac8a7f..192845b0e 100644
--- a/packages/backend/src/apps/postman/common/parameters.ts
+++ b/packages/backend/src/apps/postman/common/parameters.ts
@@ -52,6 +52,7 @@ export const transactionalEmailFields: IField[] = [
       'table',
     ],
     supportTableDisplay: true,
+    previewType: 'email' as const,
   },
   {
     label: 'Recipient email(s)',
diff --git a/packages/frontend/src/components/FlowStepTestController/index.tsx b/packages/frontend/src/components/FlowStepTestController/index.tsx
index ecacc3621..e0e91bf5c 100644
--- a/packages/frontend/src/components/FlowStepTestController/index.tsx
+++ b/packages/frontend/src/components/FlowStepTestController/index.tsx
@@ -1,4 +1,9 @@
-import { IBaseTrigger, IStep, ITriggerInstructions } from '@plumber/types'
+import {
+  IBaseTrigger,
+  IStep,
+  ITriggerInstructions,
+  TFieldPreviewType,
+} from '@plumber/types'
 
 import { useContext, useEffect, useMemo, useRef, useState } from 'react'
 import { useFormContext } from 'react-hook-form'
@@ -10,6 +15,7 @@ import {
   Icon,
   Text,
   Tooltip,
+  useDisclosure,
   VStack,
 } from '@chakra-ui/react'
 import {
@@ -25,7 +31,9 @@ import { validateStepParams } from '@/helpers/validateStepParams'
 import { useStepMetadata } from '@/hooks/useStepMetadata'
 
 import { EDITOR_MARGIN_TOP_NUM } from '../Editor/constants'
+import EmailPreviewModal from '../EmailPreviewModal'
 import ErrorResult from '../ErrorResult'
+import { substituteForPreview } from '../RichTextEditor/utils'
 import WebhookUrlInfo from '../WebhookUrlInfo'
 
 import { CheckAgainButton } from './CheckAgainButton'
@@ -38,6 +46,10 @@ import {
   matchParamsToDataIn,
 } from './utils'
 
+const PREVIEW_BUTTON_COPY: Record<TFieldPreviewType, string> = {
+  email: 'Preview email',
+}
+
 const defaultTriggerInstructions: ITriggerInstructions = {
   beforeUrlMsg: `# 1. You'll need to configure your application with this webhook URL.`,
   afterUrlMsg: `# 2. Send some data to the webhook URL after configuration. Then, click check step.`,
@@ -122,7 +134,45 @@ export default function FlowStepTestController(
     lastErrorDetails,
     isWebhookSubstep,
     testVariables,
-  } = useTestDetails(step, currentTestExecutionStep, allApps)
+    previewAction,
+  } = useTestDetails(step, currentTestExecutionStep, allApps, substeps)
+
+  const {
+    isOpen: isPreviewModalOpen,
+    onOpen: onPreviewModalOpen,
+    onClose: onPreviewModalClose,
+  } = useDisclosure()
+
+  const previewModal = useMemo(() => {
+    if (!previewAction) {
+      return null
+    }
+    switch (previewAction.kind) {
+      case 'email': {
+        const previewHtml = substituteForPreview(previewAction.html, varInfoMap)
+        return (
+          <EmailPreviewModal
+            isOpen={isPreviewModalOpen}
+            onClose={onPreviewModalClose}
+            html={previewHtml}
+          />
+        )
+      }
+    }
+  }, [previewAction, varInfoMap, isPreviewModalOpen, onPreviewModalClose])
+
+  const previewButton = previewAction ? (
+    <Button
+      variant="outline"
+      colorScheme="black"
+      size="sm"
+      onClick={onPreviewModalOpen}
+      mr={2}
+      data-test={`preview-${previewAction.kind}-button`}
+    >
+      {PREVIEW_BUTTON_COPY[previewAction.kind]}
+    </Button>
+  ) : null
   const containerRef = useRef<HTMLDivElement>(null)
   const webhookUrlInfoRef = useRef<HTMLDivElement>(null)
   const [collapseDirection, setCollapseDirection] = useState<'up' | 'down'>(
@@ -337,6 +387,7 @@ export default function FlowStepTestController(
                       {!isDirty ? 'Saved' : 'Save without checking'}
                     </Button>
                   )}
+                  {previewButton}
                   <CheckAgainButton
                     isUnstyledInfobox={isStepUnchecked}
                     onClick={handleSaveAndTest}
@@ -379,6 +430,7 @@ export default function FlowStepTestController(
                   {isDirty ? 'Save' : 'Saved'}
                 </Button>
               )}
+              {previewButton}
               <CheckStepTooltip
                 hasDeletedVars={hasDeletedVars}
                 isDisabled={shouldAllowCheckStep}
@@ -397,6 +449,7 @@ export default function FlowStepTestController(
           </VStack>
         )}
       </VStack>
+      {previewModal}
     </>
   )
 }
diff --git a/packages/frontend/src/components/FlowStepTestController/useTestDetails.ts b/packages/frontend/src/components/FlowStepTestController/useTestDetails.ts
index 5de1d898e..b7d31a605 100644
--- a/packages/frontend/src/components/FlowStepTestController/useTestDetails.ts
+++ b/packages/frontend/src/components/FlowStepTestController/useTestDetails.ts
@@ -1,21 +1,77 @@
-import { IApp, IExecutionStep, IJSONObject, IStep } from '@plumber/types'
+import {
+  IApp,
+  IExecutionStep,
+  IFieldRichText,
+  IJSONObject,
+  IStep,
+  ISubstep,
+  TFieldPreviewType,
+} from '@plumber/types'
+
+import { useMemo } from 'react'
+import { useWatch } from 'react-hook-form'
 
 import { extractVariables, Variable } from '@/helpers/variables'
 
 import { isSameAppAndAppKey } from './utils'
 
+export interface PreviewAction {
+  kind: TFieldPreviewType
+  fieldKey: string
+  html: string
+}
+
 interface UseTestDetailsResult {
   isTestSuccessful: boolean
   isWebhookSubstep: boolean
   lastErrorDetails?: IJSONObject | null
   testVariables: Variable[] | null
+  previewAction: PreviewAction | null
 }
 
+// Stable dummy field name used when no previewable arg exists in the step, so
+// useWatch is still called unconditionally and the rules-of-hooks are
+// respected.
+const PREVIEW_WATCH_STUB = '__previewActionStub__'
+
 export function useTestDetails(
   step: IStep,
   currentTestExecutionStep: IExecutionStep | null,
   allApps: IApp[],
+  substeps: ISubstep[],
 ): UseTestDetailsResult {
+  const previewableArg = useMemo<{
+    key: string
+    previewType: TFieldPreviewType
+  } | null>(() => {
+    for (const substep of substeps ?? []) {
+      for (const arg of substep.arguments ?? []) {
+        if (arg.type === 'rich-text') {
+          const rt = arg as IFieldRichText
+          if (rt.previewType) {
+            return { key: rt.key, previewType: rt.previewType }
+          }
+        }
+      }
+    }
+    return null
+  }, [substeps])
+
+  const liveValue = useWatch({
+    name: previewableArg
+      ? `parameters.${previewableArg.key}`
+      : PREVIEW_WATCH_STUB,
+  }) as unknown
+
+  const previewAction: PreviewAction | null =
+    previewableArg && typeof liveValue === 'string' && liveValue.length > 0
+      ? {
+          kind: previewableArg.previewType,
+          fieldKey: previewableArg.key,
+          html: liveValue,
+        }
+      : null
+
   const isWebhookSubstep =
     (step.appKey === 'webhook' || step.appKey === 'gathersg') &&
     Boolean(step?.webhookUrl)
@@ -26,6 +82,7 @@ export function useTestDetails(
       isWebhookSubstep,
       lastErrorDetails: null,
       testVariables: null,
+      previewAction,
     }
   }
 
@@ -45,5 +102,6 @@ export function useTestDetails(
     isWebhookSubstep,
     lastErrorDetails,
     testVariables,
+    previewAction,
   }
 }