diff --git a/src/manifest/manifest_test.ts b/src/manifest/manifest_test.ts
index 6dbbfa62..aa3db938 100644
--- a/src/manifest/manifest_test.ts
+++ b/src/manifest/manifest_test.ts
@@ -3,7 +3,7 @@ import {
   ISlackManifestRunOnSlack,
   SlackManifestType,
 } from "./types.ts";
-import { Manifest, SlackManifest } from "./mod.ts";
+import { Manifest, SlackManifest, validateOutgoingDomains } from "./mod.ts";
 import {
   DefineDatastore,
   DefineEvent,
@@ -26,6 +26,7 @@ import {
 import { DefineConnector } from "../functions/mod.ts";
 import { InternalSlackTypes } from "../schema/slack/types/custom/mod.ts";
 import { DuplicateCallbackIdError, DuplicateNameError } from "./errors.ts";
+import { assertThrows } from "https://deno.land/std@0.152.0/testing/asserts.ts";
 
 Deno.test("SlackManifestType correctly resolves to a Hosted App when runOnSlack = true", () => {
   const definition: SlackManifestType = {
@@ -1172,3 +1173,66 @@ Deno.test("Manifest throws error when CustomEvents with duplicate name are added
     assertStringIncludes(error.message, "CustomEvent");
   }
 });
+
+Deno.test("Manifest correctly parses valid domains", () => {
+  const def = {
+    outgoingDomains: [
+      "https://slack.com",
+      "http://salesforce.com",
+      "https://api.slack.com",
+    ],
+  };
+  const expected = ["slack.com", "salesforce.com", "api.slack.com"];
+
+  const definition: SlackManifestType = {
+    runOnSlack: false,
+    name: "test",
+    description: "description",
+    backgroundColor: "#FFF",
+    longDescription:
+      "The book is a roman à clef, rooted in autobiographical incidents. The story follows its protagonist, Raoul Duke, and his attorney, Dr. Gonzo, as they descend on Las Vegas to chase the American Dream...",
+    displayName: "displayName",
+    icon: "icon.png",
+    botScopes: ["channels:history", "chat:write", "commands"],
+  };
+  const manifest = Manifest(definition);
+
+  manifest.outgoing_domains = validateOutgoingDomains(
+    def.outgoingDomains || [],
+  );
+
+  assertEquals(manifest.outgoing_domains, expected);
+});
+
+Deno.test("Manifest throws error for invalid domains", () => {
+  const def = {
+    outgoingDomains: [
+      "slack",
+      "htt*ps://api.slack.com",
+      "https://api slack.com",
+    ],
+  };
+
+  assertThrows(
+    () => {
+      const definition: SlackManifestType = {
+        runOnSlack: false,
+        name: "test",
+        description: "description",
+        backgroundColor: "#FFF",
+        longDescription:
+          "The book is a roman à clef, rooted in autobiographical incidents. The story follows its protagonist, Raoul Duke, and his attorney, Dr. Gonzo, as they descend on Las Vegas to chase the American Dream...",
+        displayName: "displayName",
+        icon: "icon.png",
+        botScopes: ["channels:history", "chat:write", "commands"],
+      };
+      const manifest = Manifest(definition);
+
+      manifest.outgoing_domains = validateOutgoingDomains(
+        def.outgoingDomains || [],
+      );
+    },
+    Error,
+    "Invalid outgoing domain",
+  );
+});
diff --git a/src/manifest/mod.ts b/src/manifest/mod.ts
index 5677e7f7..abc69029 100644
--- a/src/manifest/mod.ts
+++ b/src/manifest/mod.ts
@@ -32,6 +32,30 @@ export const Manifest = (
   return manifest.export();
 };
 
+export const validateOutgoingDomains = (
+  domains: string[],
+) => {
+  return domains.map((domain) => {
+    try {
+      const url = domain.includes("://") ? domain : `http://${domain}`;
+      return new URL(url).hostname;
+    } catch (e) {
+      if (isValidDomain(domain)) {
+        return domain;
+      } else {
+        throw new Error(
+          `Invalid outgoing domain: ${domain}, error ${e}`,
+        );
+      }
+    }
+  });
+};
+
+const isValidDomain = (domain: string) => {
+  const domainPattern = /^[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*\.[a-zA-Z]{2,}$/;
+  return domainPattern.test(domain);
+};
+
 export class SlackManifest {
   constructor(private definition: SlackManifestType) {
     this.registerFeatures();
@@ -132,7 +156,9 @@ export class SlackManifest {
       );
     }
 
-    manifest.outgoing_domains = def.outgoingDomains || [];
+    manifest.outgoing_domains = validateOutgoingDomains(
+      def.outgoingDomains || [],
+    );
 
     // Assign remote hosted app properties
     if (manifest.settings.function_runtime === "slack") {