diff --git a/action.yml b/action.yml
index 38a25422..ea0d3bb2 100644
--- a/action.yml
+++ b/action.yml
@@ -54,6 +54,7 @@ inputs:
   convert_markdown:
     description: Convert body from Markdown to HTML (set content_type input as text/html too)
     required: false
+    default: "false"
   attachments:
     description: Files that will be added to mail message attachments (separated with comma)
     required: false
diff --git a/main.js b/main.js
index 9751990a..0819edaf 100644
--- a/main.js
+++ b/main.js
@@ -143,7 +143,7 @@ async function main() {
         const replyTo = core.getInput("reply_to", { required: false });
         const inReplyTo = core.getInput("in_reply_to", { required: false });
         const attachments = core.getInput("attachments", { required: false });
-        const convertMarkdown = core.getInput("convert_markdown", {
+        const convertMarkdown = core.getBooleanInput("convert_markdown", {
             required: false,
         });
         const ignoreCert = core.getInput("ignore_cert", { required: false });