feat: add postal-mime (#335)

Add [`postal-mime`](https://www.npmjs.com/package/postal-mime)

> postal-mime is an email parsing library that runs in browser
environments (including Web Workers) and serverless functions (like
Cloudflare Email Workers). It takes in a raw email message (RFC822
format) and outputs a structured object containing headers, recipients,
attachments, and more.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Chores**
	- Added a new package dependency to the project configuration.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

package.json

@@ -11530,6 +11530,9 @@
     "post-messenger": {
       "version": "*"
     },
+    "postal-mime": {
+      "version": "*"
+    },
     "postcss": {
       "version": "*"
     },