Custom Data

Adding custom data to your messages

There will be a time when you will be required to add custom data to your email messages. Example, you want to add your own ID to every messages. MimePost provides a way to add those data.

Ways to attach your Custom Data

You can add your custom key & value pairs to each email messages using:

  1. SMTP headers


SMTP Headers

You can add your custom data using "X-Vars" SMTP headers, like in below example:

X-Vars: {"user_id":"ea1fd1fd-8a4e-4e14-a8ad-ff06c6420ea1", "invoice_id": "3339d083-7cc9-4d2a-9c77-9b6e862c27b9"}

NOTE: The value of the header should be in a valid JSON format.


You can add vars hash in the JSON body of your HTTP API call, like in below example:


    "vars": {
        "user_id": "ea1fd1fd-8a4e-4e14-a8ad-ff06c6420ea1",
        "invoice_id": "3339d083-7cc9-4d2a-9c77-9b6e862c27b9"

Ways to retreive your custom data


The MimePost will pass your custom data in every event of webhook call, like below example

Delivered event Webhook call

Webhook Event Sample

Front-end & API

Your custom data won't be available from our front-end or from API, this is because we have No-data policy. As we do not store any user data, so you can not search your custom varaibles using our front-end (like emaillogs) or any get email api.

Email Messages Source

The custom data will be available in your email message source code, like any other MIME headers.


Currently we have not implement any limits, but we will add them soon. Below are the recommendations that you should follow:

  1. You should not use multiple X-Vars headers in SMTP

  2. Do not use more than 10 key value fields

  3. Total length of all the values should not be more than 255 characters