How to append Email Address to contacts currently in DB without it?

[Brian_Campbell1]

I've recently come into a new role and am working with a number of Marketo instances. Some of them have thousands of contacts without email addresses. I want to clean this up, and am working to get the emails so I can append them to the data.

My question is this:

How can I add (append) the correct email address to these contacts without completely removing them from the DB and re-uploading them with the appended email?

[SanfordWhiteman]

Export to a spreadsheet with lead ID as a column.

Fill in the email addresses.

Then either:

1. Do an API (not UI) import, which can lookup by ID.

or

2. Call a webhook for the leads and have the hook read from the file and write back the email.