Soft Bounce Error Code - Does Anyone Know What This Means?

The two explanations I've seen for this error code are: 1) indicates the recipient's server has a firewall preventing your mail from being delivered or 2) simply too much network traffic for your email to go out at that time.

I can't say for certain which the actual reason would be in this case, but the good news us soft bounces are generally temporary and clear up on their own.  Hard bounces, on the other hand, occur when your data is no longer valid, and there's not much you can really do about that other than to cycle your data from time to time.

This should help!! https://community.marketo.com/MarketoDiscussionDetail?id=90650000000Ph6TAAS

Looks like yours is congestion.

Kim

This essentially means that the message timed out for any number of reasons. it would have appeared as Pending for awhile and after 24 hours, Marketo stops re-trying soft bounces.