improvement(reply-gmail): added reply to gmail (#1809)

* added reply to thread/message

* cleanup, extract header helper for threaded replies

* more helpers

apps/sim/app/api/tools/gmail/draft/route.ts

@@ -5,7 +5,12 @@ import { createLogger } from '@/lib/logs/console/logger'
 import { processFilesToUserFiles } from '@/lib/uploads/utils/file-utils'
 import { downloadFileFromStorage } from '@/lib/uploads/utils/file-utils.server'
 import { generateRequestId } from '@/lib/utils'
-import { base64UrlEncode, buildMimeMessage } from '@/tools/gmail/utils'
+import {
+  base64UrlEncode,
+  buildMimeMessage,
+  buildSimpleEmailMessage,
+  fetchThreadingHeaders,
+} from '@/tools/gmail/utils'
 
 export const dynamic = 'force-dynamic'
 
@@ -16,8 +21,10 @@ const GMAIL_API_BASE = 'https://gmail.googleapis.com/gmail/v1/users/me'
 const GmailDraftSchema = z.object({
   accessToken: z.string().min(1, 'Access token is required'),
   to: z.string().min(1, 'Recipient email is required'),
-  subject: z.string().min(1, 'Subject is required'),
+  subject: z.string().optional().nullable(),
   body: z.string().min(1, 'Email body is required'),
+  threadId: z.string().optional().nullable(),
+  replyToMessageId: z.string().optional().nullable(),
   cc: z.string().optional().nullable(),
   bcc: z.string().optional().nullable(),
   attachments: z.array(z.any()).optional().nullable(),
@@ -49,11 +56,19 @@ export async function POST(request: NextRequest) {
 
     logger.info(`[${requestId}] Creating Gmail draft`, {
       to: validatedData.to,
-      subject: validatedData.subject,
+      subject: validatedData.subject || '',
       hasAttachments: !!(validatedData.attachments && validatedData.attachments.length > 0),
       attachmentCount: validatedData.attachments?.length || 0,
     })
 
+    const threadingHeaders = validatedData.replyToMessageId
+      ? await fetchThreadingHeaders(validatedData.replyToMessageId, validatedData.accessToken)
+      : {}
+
+    const originalMessageId = threadingHeaders.messageId
+    const originalReferences = threadingHeaders.references
+    const originalSubject = threadingHeaders.subject
+
     let rawMessage: string | undefined
 
     if (validatedData.attachments && validatedData.attachments.length > 0) {
@@ -106,8 +121,10 @@ export async function POST(request: NextRequest) {
           to: validatedData.to,
           cc: validatedData.cc ?? undefined,
           bcc: validatedData.bcc ?? undefined,
-          subject: validatedData.subject,
+          subject: validatedData.subject || originalSubject || '',
           body: validatedData.body,
+          inReplyTo: originalMessageId,
+          references: originalReferences,
           attachments: attachmentBuffers,
         })
 
@@ -117,22 +134,21 @@ export async function POST(request: NextRequest) {
     }
 
     if (!rawMessage) {
-      const emailHeaders = [
-        'Content-Type: text/plain; charset="UTF-8"',
-        'MIME-Version: 1.0',
-        `To: ${validatedData.to}`,
-      ]
+      rawMessage = buildSimpleEmailMessage({
+        to: validatedData.to,
+        cc: validatedData.cc,
+        bcc: validatedData.bcc,
+        subject: validatedData.subject || originalSubject,
+        body: validatedData.body,
+        inReplyTo: originalMessageId,
+        references: originalReferences,
+      })
+    }
 
-      if (validatedData.cc) {
-        emailHeaders.push(`Cc: ${validatedData.cc}`)
-      }
-      if (validatedData.bcc) {
-        emailHeaders.push(`Bcc: ${validatedData.bcc}`)
-      }
+    const draftMessage: { raw: string; threadId?: string } = { raw: rawMessage }
 
-      emailHeaders.push(`Subject: ${validatedData.subject}`, '', validatedData.body)
-      const email = emailHeaders.join('\n')
-      rawMessage = Buffer.from(email).toString('base64url')
+    if (validatedData.threadId) {
+      draftMessage.threadId = validatedData.threadId
     }
 
     const gmailResponse = await fetch(`${GMAIL_API_BASE}/drafts`, {
@@ -142,7 +158,7 @@ export async function POST(request: NextRequest) {
         'Content-Type': 'application/json',
       },
       body: JSON.stringify({
-        message: { raw: rawMessage },
+        message: draftMessage,
       }),
     })
 

apps/sim/app/api/tools/gmail/send/route.ts

@@ -5,7 +5,12 @@ import { createLogger } from '@/lib/logs/console/logger'
 import { processFilesToUserFiles } from '@/lib/uploads/utils/file-utils'
 import { downloadFileFromStorage } from '@/lib/uploads/utils/file-utils.server'
 import { generateRequestId } from '@/lib/utils'
-import { base64UrlEncode, buildMimeMessage } from '@/tools/gmail/utils'
+import {
+  base64UrlEncode,
+  buildMimeMessage,
+  buildSimpleEmailMessage,
+  fetchThreadingHeaders,
+} from '@/tools/gmail/utils'
 
 export const dynamic = 'force-dynamic'
 
@@ -16,8 +21,10 @@ const GMAIL_API_BASE = 'https://gmail.googleapis.com/gmail/v1/users/me'
 const GmailSendSchema = z.object({
   accessToken: z.string().min(1, 'Access token is required'),
   to: z.string().min(1, 'Recipient email is required'),
-  subject: z.string().min(1, 'Subject is required'),
+  subject: z.string().optional().nullable(),
   body: z.string().min(1, 'Email body is required'),
+  threadId: z.string().optional().nullable(),
+  replyToMessageId: z.string().optional().nullable(),
   cc: z.string().optional().nullable(),
   bcc: z.string().optional().nullable(),
   attachments: z.array(z.any()).optional().nullable(),
@@ -49,11 +56,19 @@ export async function POST(request: NextRequest) {
 
     logger.info(`[${requestId}] Sending Gmail email`, {
       to: validatedData.to,
-      subject: validatedData.subject,
+      subject: validatedData.subject || '',
       hasAttachments: !!(validatedData.attachments && validatedData.attachments.length > 0),
       attachmentCount: validatedData.attachments?.length || 0,
     })
 
+    const threadingHeaders = validatedData.replyToMessageId
+      ? await fetchThreadingHeaders(validatedData.replyToMessageId, validatedData.accessToken)
+      : {}
+
+    const originalMessageId = threadingHeaders.messageId
+    const originalReferences = threadingHeaders.references
+    const originalSubject = threadingHeaders.subject
+
     let rawMessage: string | undefined
 
     if (validatedData.attachments && validatedData.attachments.length > 0) {
@@ -106,8 +121,10 @@ export async function POST(request: NextRequest) {
           to: validatedData.to,
           cc: validatedData.cc ?? undefined,
           bcc: validatedData.bcc ?? undefined,
-          subject: validatedData.subject,
+          subject: validatedData.subject || originalSubject || '',
           body: validatedData.body,
+          inReplyTo: originalMessageId,
+          references: originalReferences,
           attachments: attachmentBuffers,
         })
 
@@ -117,22 +134,21 @@ export async function POST(request: NextRequest) {
     }
 
     if (!rawMessage) {
-      const emailHeaders = [
-        'Content-Type: text/plain; charset="UTF-8"',
-        'MIME-Version: 1.0',
-        `To: ${validatedData.to}`,
-      ]
+      rawMessage = buildSimpleEmailMessage({
+        to: validatedData.to,
+        cc: validatedData.cc,
+        bcc: validatedData.bcc,
+        subject: validatedData.subject || originalSubject,
+        body: validatedData.body,
+        inReplyTo: originalMessageId,
+        references: originalReferences,
+      })
+    }
 
-      if (validatedData.cc) {
-        emailHeaders.push(`Cc: ${validatedData.cc}`)
-      }
-      if (validatedData.bcc) {
-        emailHeaders.push(`Bcc: ${validatedData.bcc}`)
-      }
+    const requestBody: { raw: string; threadId?: string } = { raw: rawMessage }
 
-      emailHeaders.push(`Subject: ${validatedData.subject}`, '', validatedData.body)
-      const email = emailHeaders.join('\n')
-      rawMessage = Buffer.from(email).toString('base64url')
+    if (validatedData.threadId) {
+      requestBody.threadId = validatedData.threadId
     }
 
     const gmailResponse = await fetch(`${GMAIL_API_BASE}/messages/send`, {
@@ -141,7 +157,7 @@ export async function POST(request: NextRequest) {
         Authorization: `Bearer ${validatedData.accessToken}`,
         'Content-Type': 'application/json',
       },
-      body: JSON.stringify({ raw: rawMessage }),
+      body: JSON.stringify(requestBody),
     })
 
     if (!gmailResponse.ok) {

apps/sim/blocks/blocks/gmail.ts

@@ -65,7 +65,7 @@ export const GmailBlock: BlockConfig<GmailToolResponse> = {
       layout: 'full',
       placeholder: 'Email subject',
       condition: { field: 'operation', value: ['send_gmail', 'draft_gmail'] },
-      required: true,
+      required: false,
     },
     {
       id: 'body',
@@ -101,6 +101,27 @@ export const GmailBlock: BlockConfig<GmailToolResponse> = {
       mode: 'advanced',
       required: false,
     },
+    // Advanced Settings - Threading
+    {
+      id: 'threadId',
+      title: 'Thread ID',
+      type: 'short-input',
+      layout: 'full',
+      placeholder: 'Thread ID to reply to (for threading)',
+      condition: { field: 'operation', value: ['send_gmail', 'draft_gmail'] },
+      mode: 'advanced',
+      required: false,
+    },
+    {
+      id: 'replyToMessageId',
+      title: 'Reply to Message ID',
+      type: 'short-input',
+      layout: 'full',
+      placeholder: 'Gmail message ID (not RFC Message-ID) - use the "id" field from results',
+      condition: { field: 'operation', value: ['send_gmail', 'draft_gmail'] },
+      mode: 'advanced',
+      required: false,
+    },
     // Advanced Settings - Additional Recipients
     {
       id: 'cc',
@@ -241,13 +262,18 @@ export const GmailBlock: BlockConfig<GmailToolResponse> = {
     to: { type: 'string', description: 'Recipient email address' },
     subject: { type: 'string', description: 'Email subject' },
     body: { type: 'string', description: 'Email content' },
+    threadId: { type: 'string', description: 'Thread ID to reply to (for threading)' },
+    replyToMessageId: {
+      type: 'string',
+      description: 'Gmail message ID to reply to (use "id" field from results, not "messageId")',
+    },
     cc: { type: 'string', description: 'CC recipients (comma-separated)' },
     bcc: { type: 'string', description: 'BCC recipients (comma-separated)' },
     attachments: { type: 'json', description: 'Files to attach (UserFile array)' },
     // Read operation inputs
     folder: { type: 'string', description: 'Gmail folder' },
     manualFolder: { type: 'string', description: 'Manual folder name' },
-    messageId: { type: 'string', description: 'Message identifier' },
+    readMessageId: { type: 'string', description: 'Message identifier for reading specific email' },
     unreadOnly: { type: 'boolean', description: 'Unread messages only' },
     includeAttachments: { type: 'boolean', description: 'Include email attachments' },
     // Search operation inputs

apps/sim/lib/webhooks/outlook-polling-service.ts

@@ -368,7 +368,7 @@ async function processOutlookEmails(
           const simplifiedEmail: SimplifiedOutlookEmail = {
             id: email.id,
             conversationId: email.conversationId,
-            subject: email.subject || '(No Subject)',
+            subject: email.subject || '',
             from: email.from?.emailAddress?.address || '',
             to: email.toRecipients?.map((r) => r.emailAddress.address).join(', ') || '',
             cc: email.ccRecipients?.map((r) => r.emailAddress.address).join(', ') || '',

apps/sim/tools/gmail/draft.ts

@@ -28,7 +28,7 @@ export const gmailDraftTool: ToolConfig<GmailSendParams, GmailToolResponse> = {
     },
     subject: {
       type: 'string',
-      required: true,
+      required: false,
       visibility: 'user-or-llm',
       description: 'Email subject',
     },
@@ -38,6 +38,19 @@ export const gmailDraftTool: ToolConfig<GmailSendParams, GmailToolResponse> = {
       visibility: 'user-or-llm',
       description: 'Email body content',
     },
+    threadId: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description: 'Thread ID to reply to (for threading)',
+    },
+    replyToMessageId: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description:
+        'Gmail message ID to reply to - use the "id" field from Gmail Read results (not the RFC "messageId")',
+    },
     cc: {
       type: 'string',
       required: false,
@@ -69,6 +82,8 @@ export const gmailDraftTool: ToolConfig<GmailSendParams, GmailToolResponse> = {
       to: params.to,
       subject: params.subject,
       body: params.body,
+      threadId: params.threadId,
+      replyToMessageId: params.replyToMessageId,
       cc: params.cc,
       bcc: params.bcc,
       attachments: params.attachments,

apps/sim/tools/gmail/read.ts

@@ -225,6 +225,7 @@ export const gmailReadTool: ToolConfig<GmailReadParams, GmailToolResponse> = {
                   threadId: msg.threadId,
                   subject: msg.subject,
                   from: msg.from,
+                  to: msg.to,
                   date: msg.date,
                 })),
               },

apps/sim/tools/gmail/send.ts

@@ -28,7 +28,7 @@ export const gmailSendTool: ToolConfig<GmailSendParams, GmailToolResponse> = {
     },
     subject: {
       type: 'string',
-      required: true,
+      required: false,
       visibility: 'user-or-llm',
       description: 'Email subject',
     },
@@ -38,6 +38,19 @@ export const gmailSendTool: ToolConfig<GmailSendParams, GmailToolResponse> = {
       visibility: 'user-or-llm',
       description: 'Email body content',
     },
+    threadId: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description: 'Thread ID to reply to (for threading)',
+    },
+    replyToMessageId: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description:
+        'Gmail message ID to reply to - use the "id" field from Gmail Read results (not the RFC "messageId")',
+    },
     cc: {
       type: 'string',
       required: false,
@@ -69,6 +82,8 @@ export const gmailSendTool: ToolConfig<GmailSendParams, GmailToolResponse> = {
       to: params.to,
       subject: params.subject,
       body: params.body,
+      threadId: params.threadId,
+      replyToMessageId: params.replyToMessageId,
       cc: params.cc,
       bcc: params.bcc,
       attachments: params.attachments,

apps/sim/tools/gmail/types.ts

@@ -11,8 +11,10 @@ export interface GmailSendParams extends BaseGmailParams {
   to: string
   cc?: string
   bcc?: string
-  subject: string
+  subject?: string
   body: string
+  threadId?: string
+  replyToMessageId?: string
   attachments?: UserFile[]
 }
 

apps/sim/tools/gmail/utils.ts

@@ -7,6 +7,47 @@ import type {
 
 export const GMAIL_API_BASE = 'https://gmail.googleapis.com/gmail/v1/users/me'
 
+/**
+ * Fetch original message headers for threading
+ * @param messageId Gmail message ID to fetch headers from
+ * @param accessToken Gmail access token
+ * @returns Object containing threading headers (messageId, references, subject)
+ */
+export async function fetchThreadingHeaders(
+  messageId: string,
+  accessToken: string
+): Promise<{
+  messageId?: string
+  references?: string
+  subject?: string
+}> {
+  try {
+    const messageResponse = await fetch(
+      `${GMAIL_API_BASE}/messages/${messageId}?format=metadata&metadataHeaders=Message-ID&metadataHeaders=References&metadataHeaders=Subject`,
+      {
+        headers: {
+          Authorization: `Bearer ${accessToken}`,
+        },
+      }
+    )
+
+    if (messageResponse.ok) {
+      const messageData = await messageResponse.json()
+      const headers = messageData.payload?.headers || []
+
+      return {
+        messageId: headers.find((h: any) => h.name.toLowerCase() === 'message-id')?.value,
+        references: headers.find((h: any) => h.name.toLowerCase() === 'references')?.value,
+        subject: headers.find((h: any) => h.name.toLowerCase() === 'subject')?.value,
+      }
+    }
+  } catch (error) {
+    // Continue without threading headers rather than failing
+  }
+
+  return {}
+}
+
 // Helper function to process a Gmail message
 export async function processMessage(
   message: GmailMessage,
@@ -81,6 +122,7 @@ export function processMessageForSummary(message: GmailMessage): any {
       threadId: message?.threadId || '',
       subject: 'Unknown Subject',
       from: 'Unknown Sender',
+      to: '',
       date: '',
       snippet: message?.snippet || '',
     }
@@ -89,6 +131,7 @@ export function processMessageForSummary(message: GmailMessage): any {
   const headers = message.payload.headers || []
   const subject = headers.find((h) => h.name.toLowerCase() === 'subject')?.value || 'No Subject'
   const from = headers.find((h) => h.name.toLowerCase() === 'from')?.value || 'Unknown Sender'
+  const to = headers.find((h) => h.name.toLowerCase() === 'to')?.value || ''
   const date = headers.find((h) => h.name.toLowerCase() === 'date')?.value || ''
 
   return {
@@ -96,6 +139,7 @@ export function processMessageForSummary(message: GmailMessage): any {
     threadId: message.threadId,
     subject,
     from,
+    to,
     date,
     snippet: message.snippet || '',
   }
@@ -230,7 +274,10 @@ export function createMessagesSummary(messages: any[]): string {
   messages.forEach((msg, index) => {
     summary += `${index + 1}. Subject: ${msg.subject}\n`
     summary += `   From: ${msg.from}\n`
+    summary += `   To: ${msg.to}\n`
     summary += `   Date: ${msg.date}\n`
+    summary += `   ID: ${msg.id}\n`
+    summary += `   Thread ID: ${msg.threadId}\n`
     summary += `   Preview: ${msg.snippet}\n\n`
   })
 
@@ -255,6 +302,47 @@ export function base64UrlEncode(data: string | Buffer): string {
   return base64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '')
 }
 
+/**
+ * Build a simple text email message (without attachments)
+ * @param params Email parameters including recipients, subject, body, and threading info
+ * @returns Base64url encoded raw message
+ */
+export function buildSimpleEmailMessage(params: {
+  to: string
+  cc?: string | null
+  bcc?: string | null
+  subject?: string | null
+  body: string
+  inReplyTo?: string
+  references?: string
+}): string {
+  const { to, cc, bcc, subject, body, inReplyTo, references } = params
+  const emailHeaders = [
+    'Content-Type: text/plain; charset="UTF-8"',
+    'MIME-Version: 1.0',
+    `To: ${to}`,
+  ]
+
+  if (cc) {
+    emailHeaders.push(`Cc: ${cc}`)
+  }
+  if (bcc) {
+    emailHeaders.push(`Bcc: ${bcc}`)
+  }
+
+  emailHeaders.push(`Subject: ${subject || ''}`)
+
+  if (inReplyTo) {
+    emailHeaders.push(`In-Reply-To: ${inReplyTo}`)
+    const referencesChain = references ? `${references} ${inReplyTo}` : inReplyTo
+    emailHeaders.push(`References: ${referencesChain}`)
+  }
+
+  emailHeaders.push('', body)
+  const email = emailHeaders.join('\n')
+  return Buffer.from(email).toString('base64url')
+}
+
 /**
  * Build a MIME multipart message with optional attachments
  * @param params Message parameters including recipients, subject, body, and attachments
@@ -264,8 +352,10 @@ export interface BuildMimeMessageParams {
   to: string
   cc?: string
   bcc?: string
-  subject: string
+  subject?: string
   body: string
+  inReplyTo?: string
+  references?: string
   attachments?: Array<{
     filename: string
     mimeType: string
@@ -274,11 +364,10 @@ export interface BuildMimeMessageParams {
 }
 
 export function buildMimeMessage(params: BuildMimeMessageParams): string {
-  const { to, cc, bcc, subject, body, attachments } = params
+  const { to, cc, bcc, subject, body, inReplyTo, references, attachments } = params
   const boundary = generateBoundary()
   const messageParts: string[] = []
 
-  // Add headers
   messageParts.push(`To: ${to}`)
   if (cc) {
     messageParts.push(`Cc: ${cc}`)
@@ -286,11 +375,21 @@ export function buildMimeMessage(params: BuildMimeMessageParams): string {
   if (bcc) {
     messageParts.push(`Bcc: ${bcc}`)
   }
-  messageParts.push(`Subject: ${subject}`)
+  messageParts.push(`Subject: ${subject || ''}`)
+
+  if (inReplyTo) {
+    messageParts.push(`In-Reply-To: ${inReplyTo}`)
+  }
+  if (references) {
+    const referencesChain = inReplyTo ? `${references} ${inReplyTo}` : references
+    messageParts.push(`References: ${referencesChain}`)
+  } else if (inReplyTo) {
+    messageParts.push(`References: ${inReplyTo}`)
+  }
+
   messageParts.push('MIME-Version: 1.0')
 
   if (attachments && attachments.length > 0) {
-    // Multipart message with attachments
     messageParts.push(`Content-Type: multipart/mixed; boundary="${boundary}"`)
     messageParts.push('')
     messageParts.push(`--${boundary}`)
@@ -300,7 +399,6 @@ export function buildMimeMessage(params: BuildMimeMessageParams): string {
     messageParts.push(body)
     messageParts.push('')
 
-    // Add each attachment
     for (const attachment of attachments) {
       messageParts.push(`--${boundary}`)
       messageParts.push(`Content-Type: ${attachment.mimeType}`)
@@ -308,7 +406,6 @@ export function buildMimeMessage(params: BuildMimeMessageParams): string {
       messageParts.push('Content-Transfer-Encoding: base64')
       messageParts.push('')
 
-      // Split base64 content into 76-character lines (MIME standard)
       const base64Content = attachment.content.toString('base64')
       const lines = base64Content.match(/.{1,76}/g) || []
       messageParts.push(...lines)
@@ -317,7 +414,6 @@ export function buildMimeMessage(params: BuildMimeMessageParams): string {
 
     messageParts.push(`--${boundary}--`)
   } else {
-    // Simple text message without attachments
     messageParts.push('Content-Type: text/plain; charset="UTF-8"')
     messageParts.push('MIME-Version: 1.0')
     messageParts.push('')