{"templateId":"markdown","sharedDataIds":{"sidebar":"sidebar-docs/email-api/sidebars.yaml"},"props":{"metadata":{"markdoc":{"tagList":["admonition","tabs","tab"]},"type":"markdown"},"seo":{"title":"Add Email Headers - Mailjet Send API v3","siteUrl":"https://dev.mailjet.com/","projectTitle":"Mailjet Developer Documentation","description":"Add custom SMTP headers to transactional emails using the Mailjet Send API v3 Headers property, including a Reply-To example and full code samples.","image":"https://dev.mailjet.com/og-image.png","lang":"en-US","keywords":["Mailjet API","Email API","Content API","SMTP Relay","transactional email","email delivery","Send API","email templates","developer documentation"],"meta":[{"name":"og:type","content":"website"},{"name":"og:site_name","content":"Mailjet Developer Documentation"},{"name":"twitter:card","content":"summary_large_image"},{"name":"robots","content":"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1"},{"name":"googlebot","content":"index, follow, max-snippet:-1, max-image-preview:large"}],"jsonLd":{"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://dev.mailjet.com/#organization","name":"Mailjet","alternateName":"Sinch Mailjet","url":"https://www.mailjet.com","logo":"https://assets.mailjet.com/lib/images/mailjetLogo/mj_logo_with_text_color.png","parentOrganization":{"@type":"Organization","name":"Sinch","url":"https://www.sinch.com"}},{"@type":"WebSite","@id":"https://dev.mailjet.com/#website","name":"Mailjet Developer Documentation","description":"Official developer documentation for the Mailjet Email API, Content API and SMTP Relay.","url":"https://dev.mailjet.com/","inLanguage":"en-US","publisher":{"@id":"https://dev.mailjet.com/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://dev.mailjet.com/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]},"llmstxt":{"hide":false,"title":"Mailjet Developer Documentation","description":"Developer documentation for the Mailjet Email API, Content API and SMTP Relay - guides, API references and code samples for sending, templating and tracking email at scale.","details":{"content":"Mailjet (part of Sinch) provides APIs for sending and managing email.\n\nThis documentation covers four main areas:\n\n- **Email API** - the Send API (v3 and v3.1) for transactional and marketing email,\n  plus contact management, segmentation, campaigns, statistics, webhooks, the Parse API\n  and the Mailjet Templating Language.\n- **Content API** - programmatic management of email templates, template contents,\n  images, labels and authentication tokens (v1).\n- **SMTP Relay** - sending through Mailjet's SMTP servers, including custom headers.\n- **API Reference** - the complete, generated reference for every endpoint, built directly\n  from the OpenAPI specifications.\n\nBase URL for all REST APIs: `https://api.mailjet.com`.\nAuthentication uses HTTP Basic auth with an API key and secret key.\n\n## Machine-readable entry points\n\nPrefer these when you need the API surface in as few requests as possible:\n\n- `/openapi/openapi-mailjet.md` - the **complete** Email API reference (every endpoint,\n  grouped by resource) as a single Markdown document.\n- `/openapi/openapi-passport.md` - the **complete** Content API reference as a single\n  Markdown document.\n- `/_bundle/openapi/openapi-mailjet.yaml` - the raw, fully bundled OpenAPI 3 description\n  of the Email API.\n- `/_bundle/openapi/openapi-passport.yaml` - the raw, fully bundled OpenAPI 3 description\n  of the Content API.\n- `/sitemap.xml` - every indexable URL on this site.\n\nEvery page on this site is also available as clean Markdown by appending `.md` to its URL."},"sections":[{"title":"Email API","description":"Sending, contacts, campaigns, statistics, webhooks and templating.","includeFiles":["docs/email-api/**/*.md"],"excludeFiles":[]},{"title":"Content API","description":"Manage templates, template contents, images, labels and tokens.","includeFiles":["docs/content-api/**/*.md","docs/content-api.md"],"excludeFiles":[]},{"title":"SMTP Relay","description":"Send email through Mailjet's SMTP servers.","includeFiles":["docs/smtp-relay/**/*.md"],"excludeFiles":[]},{"title":"API Reference","description":"Complete generated reference for every Mailjet API endpoint.","includeFiles":["openapi/openapi-mailjet.yaml","openapi/openapi-passport.yaml","docs/api-reference/**/*.md"],"excludeFiles":[]},{"title":"Migrating from Mandrill","description":"Guides for switching from Mandrill to Mailjet.","includeFiles":["docs/mandrill/**/*.md"],"excludeFiles":[]}],"excludeFiles":[]}},"dynamicMarkdocComponents":[],"compilationErrors":[],"ast":{"$$mdtype":"Tag","name":"article","attributes":{},"children":[{"$$mdtype":"Tag","name":"Admonition","attributes":{"type":"info","name":"Info"},"children":[{"$$mdtype":"Tag","name":"p","attributes":{},"children":["The following adheres to Send API v3.0"]}]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":1,"id":"add-email-headers","__idx":0},"children":["Add Email Headers"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["In every message, you can specify your own Email headers using the Headers property. For example, it is possible to specify a ",{"$$mdtype":"Tag","name":"code","attributes":{},"children":["Reply-To"]}," email address."]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":3,"id":"example","__idx":1},"children":["Example"]},{"$$mdtype":"Tag","name":"Tabs","attributes":{"size":"medium"},"children":[{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"cURL","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"shell","header":{"controls":{"copy":{}}},"source":"# This call sends an email to one recipient with a Reply-To address.\ncurl -s \\\n\t-X POST \\\n\t--user \"$MJ_APIKEY_PUBLIC:$MJ_APIKEY_PRIVATE\" \\\n\thttps://api.mailjet.com/v3/send \\\n\t-H 'Content-Type: application/json' \\\n\t-d '{\n\t\t\"FromEmail\":\"pilot@mailjet.com\",\n\t\t\"FromName\":\"Mailjet Pilot\",\n\t\t\"Subject\":\"Your email flight plan!\",\n\t\t\"Text-part\":\"Dear passenger, welcome to Mailjet! May the delivery force be with you!\",\n\t\t\"Html-part\":\"<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!\",\n\t\t\"Recipients\":[{\"Email\":\"passenger@mailjet.com\"}],\n\t\t\"Headers\" : {\"Reply-To\":\"copilot@mailjet.com\"}\n\t}'\n","lang":"shell"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"PHP","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"php","header":{"controls":{"copy":{}}},"source":"<?php\nrequire 'vendor/autoload.php';\nuse \\Mailjet\\Resources;\n$mj = new \\Mailjet\\Client(getenv('MJ_APIKEY_PUBLIC'), getenv('MJ_APIKEY_PRIVATE'));\n$body = [\n    'FromEmail' => \"pilot@mailjet.com\",\n    'FromName' => \"Mailjet Pilot\",\n    'Subject' => \"Your email flight plan!\",\n    'Text-part' => \"Dear passenger, welcome to Mailjet! May the delivery force be with you!\",\n    'Html-part' => \"<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!\",\n    'Recipients' => [\n        [\n            'Email' => \"passenger@mailjet.com\"\n        ]\n    ],\n    'Headers' => [\n        'Reply-To' => \"copilot@mailjet.com\"\n    ]\n];\n$response = $mj->post(Resources::$Email, ['body' => $body]);\n$response->success() && var_dump($response->getData());\n?>\n","lang":"php"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"Node.js","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"javascript","header":{"controls":{"copy":{}}},"source":"/**\n *\n * This call sends an email to one recipient with a Reply-To address.\n *\n */\nconst mailjet = require('node-mailjet').connect(\n  process.env.MJ_APIKEY_PUBLIC,\n  process.env.MJ_APIKEY_PRIVATE\n)\nconst request = mailjet.post('send').request({\n  FromEmail: 'pilot@mailjet.com',\n  FromName: 'Mailjet Pilot',\n  Subject: 'Your email flight plan!',\n  'Text-part':\n    'Dear passenger, welcome to Mailjet! May the delivery force be with you!',\n  'Html-part':\n    '<h3>Dear passenger, welcome to <a href=\"https://www.mailjet.com/\">Mailjet</a>!<br />May the delivery force be with you!',\n  Recipients: [{ Email: 'passenger@mailjet.com' }],\n  Headers: { 'Reply-To': 'copilot@mailjet.com' },\n})\nrequest\n  .then(result => {\n    console.log(result.body)\n  })\n  .catch(error => {\n    console.log(error.statusCode)\n  })\n","lang":"javascript"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"Ruby","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"ruby","header":{"controls":{"copy":{}}},"source":"Mailjet.configure do |config|\n  config.api_key = ENV['MJ_APIKEY_PUBLIC']\n  config.secret_key = ENV['MJ_APIKEY_PRIVATE']\n  config.default_from = 'your default sending address'\nend\nvariable = Mailjet::Send.create(\n  from_email: 'pilot@mailjet.com',\n  from_name: 'Mailjet Pilot',\n  subject: 'Your email flight plan!',\n  text_part: 'Dear passenger, welcome to Mailjet! May the delivery force be with you!',\n  html_part: '<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!',\n  headers: {'Reply-To' => 'copilot@mailjet.com'},\n  recipients:[{'Email' => 'passenger@mailjet.com'}])\n","lang":"ruby"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"Python","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"python","header":{"controls":{"copy":{}}},"source":"from mailjet_rest import Client\nimport os\napi_key = os.environ['MJ_APIKEY_PUBLIC']\napi_secret = os.environ['MJ_APIKEY_PRIVATE']\nmailjet = Client(auth=(api_key, api_secret))\ndata = {\n\t\"FromEmail\":\"pilot@mailjet.com\",\n\t\"FromName\":\"Mailjet Pilot\",\n\t\"Subject\":\"Your email flight plan!\",\n\t\"Text-part\":\"Dear passenger, welcome to Mailjet! May the delivery force be with you!\",\n\t\"Html-part\":\"<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!\",\n\t\"Recipients\":[{\"Email\":\"passenger@mailjet.com\"}],\n\t\"Headers\":  {\"Reply-To\":\"copilot@mailjet.com\"}\n}\nresult = mailjet.send.create(data=data)\nprint result.status_code\nprint result.json()\n","lang":"python"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"Java","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"java","header":{"controls":{"copy":{}}},"source":"package MyClass;\nimport com.mailjet.client.errors.MailjetException;\nimport com.mailjet.client.errors.MailjetSocketTimeoutException;\nimport com.mailjet.client.MailjetClient;\nimport com.mailjet.client.MailjetRequest;\nimport com.mailjet.client.MailjetResponse;\nimport com.mailjet.client.resource.Email;\nimport org.json.JSONArray;\nimport org.json.JSONObject;\npublic class MyClass {\n    /**\n     * This call sends an email to one recipient with a Reply-To address.\n     */\n    public static void main(String[] args) throws MailjetException, MailjetSocketTimeoutException {\n      MailjetClient client;\n      MailjetRequest request;\n      MailjetResponse response;\n      client = new MailjetClient(System.getenv(\"MJ_APIKEY_PUBLIC\"), System.getenv(\"MJ_APIKEY_PRIVATE\"));\n      request = new MailjetRequest(Email.resource)\n\t\t\t\t\t\t.property(Email.FROMEMAIL, \"pilot@mailjet.com\")\n\t\t\t\t\t\t.property(Email.FROMNAME, \"Mailjet Pilot\")\n\t\t\t\t\t\t.property(Email.SUBJECT, \"Your email flight plan!\")\n\t\t\t\t\t\t.property(Email.TEXTPART, \"Dear passenger, welcome to Mailjet! May the delivery force be with you!\")\n\t\t\t\t\t\t.property(Email.HTMLPART, \"<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!\")\n\t\t\t\t\t\t.property(Email.RECIPIENTS, new JSONArray()\n                .put(new JSONObject()\n                    .put(\"Email\", \"passenger@mailjet.com\")))\n\t\t\t\t\t\t.property(Email.HEADERS, new JSONObject()\n                .put(\"Reply-To\", \"copilot@mailjet.com\"));\n      response = client.post(request);\n      System.out.println(response.getStatus());\n      System.out.println(response.getData());\n    }\n}\n","lang":"java"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"Go","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"go","header":{"controls":{"copy":{}}},"source":"/*\nThis call sends an email to one recipient with a Reply-To address.\n*/\npackage main\nimport (\n\t\"fmt\"\n\t. \"github.com/mailjet/mailjet-apiv3-go\"\n\t\"os\"\n)\nfunc main () {\n\tmailjetClient := NewMailjetClient(os.Getenv(\"MJ_APIKEY_PUBLIC\"), os.Getenv(\"MJ_APIKEY_PRIVATE\"))\n\temail := &InfoSendMail {\n      FromEmail: \"pilot@mailjet.com\",\n      FromName: \"Mailjet Pilot\",\n      Subject: \"Your email flight plan!\",\n      TextPart: \"Dear passenger, welcome to Mailjet! May the delivery force be with you!\",\n      HTMLPart: \"<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!\",\n      Recipients: []Recipient {\n        Recipient {\n          Email: \"passenger@mailjet.com\",\n        },\n      },\n      Headers: map[string]string {\n        \"ReplyTo\": \"copilot@mailjet.com\",\n      },\n    }\n\tres, err := mailjetClient.SendMail(email)\n\tif err != nil {\n\t\t\tfmt.Println(err)\n\t} else {\n\t\t\tfmt.Println(\"Success\")\n\t\t\tfmt.Println(res)\n\t}\n}\n","lang":"go"},"children":[]}]},{"$$mdtype":"Tag","name":"TabItemFragment","attributes":{"label":"C#","disable":false},"children":[{"$$mdtype":"Tag","name":"CodeBlock","attributes":{"data-language":"csharp","header":{"controls":{"copy":{}}},"source":"using Mailjet.Client;\nusing Mailjet.Client.Resources;\nusing System;\nusing Newtonsoft.Json.Linq;\nnamespace Mailjet.ConsoleApplication\n{\n   class Program\n   {\n      /// <summary>\n      /// This call sends an email to one recipient with a Reply-To address\n      /// </summary>\n      static void Main(string[] args)\n      {\n         RunAsync().Wait();\n      }\n      static async Task RunAsync()\n      {\n         MailjetClient client = new MailjetClient(Environment.GetEnvironmentVariable(\"MJ_APIKEY_PUBLIC\"), Environment.GetEnvironmentVariable(\"MJ_APIKEY_PRIVATE\"));\n         MailjetRequest request = new MailjetRequest\n         {\n            Resource = Send.Resource,\n         }\n            .Property(Send.FromEmail, \"pilot@mailjet.com\")\n            .Property(Send.FromName, \"Mailjet Pilot\")\n            .Property(Send.Subject, \"Your email flight plan!\")\n            .Property(Send.TextPart, \"Dear passenger, welcome to Mailjet! May the delivery force be with you!\")\n            .Property(Send.HtmlPart, \"<h3>Dear passenger, welcome to <a href=\\\"https://www.mailjet.com/\\\">Mailjet</a>!<br />May the delivery force be with you!\")\n            .Property(Send.Recipients, new JArray {\n                new JObject {\n                 {\"Email\", \"passenger@mailjet.com\"}\n                 }\n                })\n            .Property(Send.Headers, new JObject {\n                {\"Reply-To\", \"copilot@mailjet.com\"}\n                });\n         MailjetResponse response = await client.PostAsync(request);\n         if (response.IsSuccessStatusCode)\n         {\n            Console.WriteLine(string.Format(\"Total: {0}, Count: {1}\\n\", response.GetTotal(), response.GetCount()));\n            Console.WriteLine(response.GetData());\n         }\n         else\n         {\n            Console.WriteLine(string.Format(\"StatusCode: {0}\\n\", response.StatusCode));\n            Console.WriteLine(string.Format(\"ErrorInfo: {0}\\n\", response.GetErrorInfo()));\n            Console.WriteLine(string.Format(\"ErrorMessage: {0}\\n\", response.GetErrorMessage()));\n         }\n      }\n   }\n}\n","lang":"csharp"},"children":[]}]}]}]},"headings":[{"value":"Add Email Headers","id":"add-email-headers","depth":1},{"value":"Example","id":"example","depth":3}],"frontmatter":{"title":"Mailjet Send API v3.0","seo":{"title":"Add Email Headers - Mailjet Send API v3","description":"Add custom SMTP headers to transactional emails using the Mailjet Send API v3 Headers property, including a Reply-To example and full code samples."}},"lastModified":"2026-08-26T10:53:57.000Z","pagePropGetterError":{"message":"","name":""}},"slug":"/docs/email-api/send-api-v3/add-email-headers","userData":{"isAuthenticated":false,"teams":["anonymous"]},"isPublic":true}