In your email link performance reports, you may see a line for a "malformed link." Here's how that happens:
When Marketo sends a link in an email, we change the link in the back end before the email is processed to include tracking information that uniquely identifies the lead to whom the message was sent. As part of the linked URL, we use a token that says mkt_tok= and then a long string of letters and numbers that uniquely identifies the specific lead. This allows us to trace which lead clicked which link.
Normally, the token gets passed through the email link and into the URL of the originally linked location. You may see links that say something like www.yourdomain.com/yoursite?mkt_tok=kjnt98h09th8knt09voneg89p - this means that the lead identified by that long string went to www.yourdomain.com/yoursite.
Sometimes, an email program, anti-spam filter, or browser will mangle the token that identifies your lead. The token is the last piece of a Marketo email link, and can sometimes get cut off for length. When this happens, Marketo is not able to trace the unique lead that clicked the link, so our reports will display malformed link.
Malformed links are not due to any misconfiguration on your part. Rather, they are an artifact that is a consequence of your lead's email system or browser not passing the link correctly.