See http://www.slideshare.net/jdavidhill/marketo-email-reputation-management
for some help.
Yes, Marketo does try soft bounces again, but only up to 24hrs. I forget how many times it tries. It might be on a scale:
First Try
wait 1h
Second Try
Wait 4h
Third Try
Wait 6h...
There are some possibilities here, but it's hard to tell from here :)
- You are now on a shared IP with some less than stellar senders. Before you were on a dedicated IP. You can ask marketo to move you over to a different IP with better senders
- Since you switched, the world doesn't know you as well
- you did not install DKIM/SPF for Marketo yet. Go to Admin > Email > DKIM
- Something changed in the way you segment the list or permissions.
- you have a lot of personal email domains and now those domains don't see you as a trusted sender anymore. Marketo emails do get throttled by yahoo and gmail.