Send Gmail Messages with Custom Aliases and Attachments via API

The workflow JSON

Copy or download the full n8n JSON below. Paste it into a new n8n workflow, add your credentials, activate. Full import guide →

{
  "nodes": [
    {
      "id": "f3959088-8592-4a56-bd3e-c09a5400d0b7",
      "name": "Send Gmail as Alias",
      "type": "n8n-nodes-base.httpRequest",
      "position": [
        320,
        -120
      ],
      "parameters": {
        "url": "https://gmail.googleapis.com/gmail/v1/users/me/messages/send",
        "method": "POST",
        "options": {},
        "sendBody": true,
        "authentication": "predefinedCredentialType",
        "bodyParameters": {
          "parameters": [
            {
              "name": "raw",
              "value": "={{ $json.encoded_message }}"
            }
          ]
        },
        "nodeCredentialType": "gmailOAuth2"
      },
      "credentials": {
        "gmailOAuth2": {
          "name": "<your credential>"
        }
      },
      "executeOnce": true,
      "typeVersion": 4.2
    },
    {
      "id": "1e88749c-f3fd-4c56-8db2-db101855088e",
      "name": "Format Email Payload",
      "type": "n8n-nodes-base.code",
      "position": [
        100,
        -125
      ],
      "parameters": {
        "jsCode": "// ===========================\n// FIELD VALIDATION\n// ===========================\n// Define which fields are absolutely required for sending an email\nconst requiredFields = ['fromEmail', 'toEmail', 'subject', 'htmlBody'];\nconst inputData = $input.first().json.body;\nconst missingFields = [];\n\n// Check each required field to ensure it exists and has a value\nrequiredFields.forEach(field => {\n if (!inputData[field]) {\n   missingFields.push(field);\n }\n});\n\n// If any required fields are missing, throw an error immediately\nif (missingFields.length > 0) {\n throw new Error(`Missing required fields: ${missingFields.join(', ')}`);\n}\n\n// ===========================\n// EMAIL CONFIGURATION SETUP\n// ===========================\n// Build email configuration object with required fields and optional fields\n// Optional fields will be null if not provided, required fields are guaranteed to exist\nconst emailConfig = {\n senderName: inputData.senderName || null,    // Optional: Display name for sender\n fromEmail: inputData.fromEmail,              // Required: Email address to send from (must be verified alias)\n replyTo: inputData.replyTo || null,          // Optional: Different reply-to address\n toEmail: inputData.toEmail,                  // Required: Recipient email address\n subject: inputData.subject,                  // Required: Email subject line\n htmlBody: inputData.htmlBody                 // Required: HTML content of the email\n};\n\n// ===========================\n// DEBUG LOGGING\n// ===========================\n// Log all available data to help troubleshoot issues\nconsole.log('Available data:', JSON.stringify($input.all(), null, 2));\nconsole.log('Binary keys:', Object.keys($binary || {}));\nconsole.log('Binary data:', $binary);\n\n// ===========================\n// ATTACHMENT PROCESSING\n// ===========================\n// Get all binary data keys from the previous node (files to attach)\nconst binaryKeys = Object.keys($binary || {});\nconst attachments = [];\n\n// Process each binary file found in the $binary object\nbinaryKeys.forEach(key => {\n const binaryFile = $binary[key];\n console.log(`Processing binary key: ${key}`, binaryFile);\n \n // Only add files that have actual data\n if (binaryFile && binaryFile.data) {\n   attachments.push({\n     data: binaryFile.data,                                    // Base64 encoded file data\n     fileName: binaryFile.fileName || `${key}.pdf`,           // Use original filename or create one\n     mimeType: binaryFile.mimeType || 'application/pdf'       // Use detected MIME type or default to PDF\n   });\n }\n});\n\nconsole.log('Processed attachments:', attachments.length);\n\n// ===========================\n// FALLBACK ATTACHMENT DETECTION\n// ===========================\n// If no attachments found using $binary, try alternative approach\n// Some nodes might store binary data in item.binary instead\nif (attachments.length === 0) {\n console.log('No attachments found in $binary, trying alternative approach...');\n \n // Try accessing the data property directly from the input item\n const item = $input.first();\n if (item.binary && Object.keys(item.binary).length > 0) {\n   console.log('Found binary data in item.binary');\n   \n   Object.keys(item.binary).forEach(key => {\n     const binaryFile = item.binary[key];\n     attachments.push({\n       data: binaryFile.data,\n       fileName: binaryFile.fileName || `${key}.pdf`,\n       mimeType: binaryFile.mimeType || 'application/pdf'\n     });\n   });\n }\n}\n\n// ===========================\n// HTML BODY PROCESSING\n// ===========================\n// Replace any {{FILE_COUNT}} placeholder in the HTML with actual attachment count\nconst updatedHtmlBody = emailConfig.htmlBody.replace('{{FILE_COUNT}}', attachments.length);\n\n// ===========================\n// MIME MESSAGE CONSTRUCTION\n// ===========================\n// Generate a unique boundary string for the multipart MIME message\n// This separates different parts of the email (body, attachments, etc.)\nconst boundary = `----=_Part_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;\n\n// ===========================\n// EMAIL HEADERS AND STRUCTURE\n// ===========================\n// Build the complete email message in RFC2822 format\n// Start with headers and basic structure\nlet emailMessage = `From: ${emailConfig.senderName ? `\"${emailConfig.senderName}\" <${emailConfig.fromEmail}>` : emailConfig.fromEmail}\nTo: ${emailConfig.toEmail}${emailConfig.replyTo ? `\\nReply-To: ${emailConfig.replyTo}` : ''}\nSubject: ${emailConfig.subject}\nMIME-Version: 1.0\nContent-Type: multipart/mixed; boundary=\"${boundary}\"\n\n--${boundary}\nContent-Type: text/html; charset=utf-8\nContent-Transfer-Encoding: 7bit\n\n${updatedHtmlBody}\n\n`;\n\n// ===========================\n// ATTACHMENT ADDITION\n// ===========================\n// Add each attachment as a separate MIME part\nattachments.forEach(attachment => {\n console.log(`Adding attachment: ${attachment.fileName}`);\n \n emailMessage += `--${boundary}\nContent-Type: ${attachment.mimeType}; name=\"${attachment.fileName}\"\nContent-Disposition: attachment; filename=\"${attachment.fileName}\"\nContent-Transfer-Encoding: base64\n\n${attachment.data}\n\n`;\n});\n\n// ===========================\n// MIME MESSAGE FINALIZATION\n// ===========================\n// Close the multipart message with the final boundary\nemailMessage += `--${boundary}--`;\n\n// ===========================\n// GMAIL API ENCODING\n// ===========================\n// Gmail API requires the entire message to be base64url encoded\n// Base64url is like base64 but uses - instead of + and _ instead of /\n// and removes padding (=) characters\nconst encodedMessage = Buffer.from(emailMessage, 'utf8')\n .toString('base64')           // Convert to base64\n .replace(/\\+/g, '-')          // Replace + with -\n .replace(/\\//g, '_')          // Replace / with _\n .replace(/=/g, '');           // Remove padding\n\n// ===========================\n// RETURN RESULTS\n// ===========================\n// Return the encoded message for the Gmail API and debug information\nreturn {\n encoded_message: encodedMessage,              // This goes to the Gmail API\n debug_info: {                                 // This helps with troubleshooting\n   attachments_count: attachments.length,\n   attachment_names: attachments.map(a => a.fileName),\n   binary_keys_found: binaryKeys,\n   has_binary: !!$binary,\n   input_keys: Object.keys($input.first() || {}),\n   email_config: {\n     has_sender_name: !!emailConfig.senderName,\n     has_reply_to: !!emailConfig.replyTo,\n     from: emailConfig.fromEmail,\n     to: emailConfig.toEmail,\n     subject: emailConfig.subject\n   }\n }\n};"
      },
      "executeOnce": true,
      "typeVersion": 2
    },
    {
      "id": "92c047a3-da23-4dbf-96a1-257384d50566",
      "name": "Split Out Attachments",
      "type": "n8n-nodes-base.splitOut",
      "position": [
        -340,
        -200
      ],
      "parameters": {
        "include": "allOtherFields",
        "options": {},
        "fieldToSplitOut": "body.file_urls"
      },
      "typeVersion": 1
    },
    {
      "id": "abd6a0b8-4abb-4f41-a441-2e666aff0311",
      "name": "If Attachments",
      "type": "n8n-nodes-base.if",
      "position": [
        -560,
        -125
      ],
      "parameters": {
        "options": {},
        "conditions": {
          "options": {
            "version": 2,
            "leftValue": "",
            "caseSensitive": true,
            "typeValidation": "strict"
          },
          "combinator": "and",
          "conditions": [
            {
              "id": "f293e2a3-4cba-48e9-8c8d-43119df14d57",
              "operator": {
                "type": "array",
                "operation": "notEmpty",
                "singleValue": true
              },
              "leftValue": "={{ $json.body.file_urls }}",
              "rightValue": ""
            }
          ]
        }
      },
      "typeVersion": 2.2
    },
    {
      "id": "5ead651a-836e-411a-80ae-5a0af1236eec",
      "name": "Download Attachments",
      "type": "n8n-nodes-base.httpRequest",
      "position": [
        -120,
        -125
      ],
      "parameters": {
        "url": "={{ $json['body.file_urls'] }}",
        "options": {}
      },
      "typeVersion": 4.2
    },
    {
      "id": "f3ae4375-1a9c-4348-8003-13930fc613a7",
      "name": "Webhook Trigger",
      "type": "n8n-nodes-base.webhook",
      "position": [
        -780,
        -125
      ],
      "parameters": {
        "path": "send-gmail-as-alias",
        "options": {},
        "httpMethod": "POST",
        "responseMode": "lastNode"
      },
      "typeVersion": 2
    }
  ],
  "connections": {
    "If Attachments": {
      "main": [
        [
          {
            "node": "Split Out Attachments",
            "type": "main",
            "index": 0
          }
        ],
        [
          {
            "node": "Download Attachments",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Webhook Trigger": {
      "main": [
        [
          {
            "node": "If Attachments",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Download Attachments": {
      "main": [
        [
          {
            "node": "Format Email Payload",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Format Email Payload": {
      "main": [
        [
          {
            "node": "Send Gmail as Alias",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Split Out Attachments": {
      "main": [
        [
          {
            "node": "Download Attachments",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  }
}

Credentials you'll need

Each integration node will prompt for credentials when you import. We strip credential IDs before publishing — you'll add your own.

• gmailOAuth2

About this workflow

Since the native Gmail node has some limitations regarding use of email aliases, this template allows you to set up your own internal endpoint/sub-workflow to send emails as an email alias .

Source: https://n8n.io/workflows/5613/ — original creator credit. Request a take-down →

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