I have recently sent out an email to our customers but the Subject line looks weird, with a Marketo link to it.
Does anyone have any idea why this is happening?
You'd have to show us the HTML source (in Marketo and the source of the received email in the Inbox) to look into this.
At a glance it looks like the preheader has a link in it but you haven't shown nearly enough.
Retrieving data ...