Passing unique lead ID to 3rd party URL and using it in follow-up smart list in Marketo

[Jason_Reber__TH]

Hi all,

I am sending the same "sruvey request" email via Marketo to a different group of a few hundred leads every 1 week for the next 2 months.
This email will have a link to a 3rd party landing page with a survey on it.
The platform that hosts the survey doesn't collect a user's email address or name, but I want to know which of the users I sent the survey request email to actually completed the survey, on order to then send them a thank you email.

To do this I was going to simply append the Lead.ID or similar to the querystring of the link in my survey request email, like so:

http://www.example.com/path/name/?mktId={{lead.Id}}

The 3rd party platform is able to capture that parameter value on their side and then I am able to login to the 3rd party platform at the end of each week to pull a list of all the unique Marketo IDs who completed the survey.
Ideally I could then use that list of IDs in Marketo in the smart list for an email program to know who to send the thank you email to.

But the Lead.ID field doesn't seem to be available to me when I am building out the thank you email smart list.

I noticed Marketo has other unique identifier fields such as Marketo Unique Name and Marketo Unique Code.

Which unique identifier field can I use in both the outgoing "survey request" email and in the smart list I use to find the people who completed the survey?

Any solutions or suggestions greatly appreciated...

[SanfordWhiteman · Accepted solution]

At least 4 ways to go about this:

1. Maintain a mirror field. Regularly copy the {{Lead.ID}} to another, custom String field using Change Data Value. Then that custom field can be used in Smart Lists. Or same idea with {{Lead.Marketo Unique Code}}.
2. Include an encrypted form of the Email Address using an reversible algorithm (AES for example), decrypt after downloading, then use the Email Address in Smart Lists as usual. This option would make it impossible for the end user to know the original text you'd encoded.
3. include a merely encoded form of the Email Address using the ubiquitous Base64 algorithm. This isn't real encryption and the end user themselves could turn, say c2FuZHlAZXhhbXBsZS5jb20= back into sandy@example.com if they so desired. But it's likely a lot easier for you to accomplish, and will stay as gibberish for most users. For example, I put up this quick Google Sheet which Base64-encodes email addresses.
4. An API-based upload, using the Lead ID as the lookup key, which adds people to a list. Requires a developer with Marketo knowledge.

[SanfordWhiteman]

btw the Apps Script in that Sheet is only

function base64(input,direction) {
  return direction === "decode" ? Utilities.base64DecodeWebSafe(input) : Utilities.base64EncodeWebSafe(input);
}

[Jason_Reber__TH]

This is excellent info, Sanford, thank you. I'll roll with the mirror field approach.