What is the harm to send emails without DKIM setup?

Hi Patrick,

Yes, it may. A DKIM autenticates and signs an email. It's a recommended and one of the best practice as it validates your signature. Legitimate mail from known sources that is signed will be delivered. In the words of Josh, All DKIM and SPF records do is tell the internet (and the target email server) that you said it is ok for Marketo to send email on your behalf. I would recommend setting up DKIM before you send email. 

Hope this helps!

Hi Alok, thanks for the fast response. I understand that if we send it without DKIM, the emails will more quickly be seen as spam. However our sending is time sensitive so we can't wait too long. Marketo tells me it takes two weeks to set DKIM up.

If I send an email now, without DKIM, and then have it set up in two week, will this first email influence future delivery of emails?

TIA

No, it does not necessarily influence future emails.

DKIM provides a method for validating a domain name identity that is associated with a message through cryptographic authentication.

The Sender Policy Framework (SPF) is an open standard specifying a technical method to prevent sender address forgery. In short, it identifies the sender as genuine.

IT Operations usually processes DNS changes/updates once a week to minimise impact on production systems. 
If you log a DKIM request in the middle of the week there is a reasonable probability to have that completed after the weekend mantainance. Please note that is a guideline only.