On October 19th we had unusual low deliverability - 86% - and we noticed that such cases always happen when Marketo releases updates.
Did somebody experience now the same thing with deliverability?
We work with the same base which usually shows deliverability 90-95%.
Northing here as well.
On a similar topic, a while ago we had the similar experience, with a sudden increase in suspended emails (Josh Hill wrote a detailed list of reasons why this could happen), but in our case the delivery rate went back up to normal in future campaigns. Check out the server responses for undelivered emails (hard bounces/soft bounces, maybe some emails still pending?).
You could ask Support if you really believe an update broke something. They did have a couple of issues with emailing on some pods.
Remember that Deliverability != inbox rate and is tied to many factors that probably aren't related to Marketo's software update.
Josh makes a good point. Often times the deliverability rate is nowhere near the % of emails that actually make into the users' inbox (especially if you're sending emails to multiple people at the same account). In many situations, spam filters will re-route the emails to a quarantine area and not even deliver to the intended user. But this will still show up as being "delivered" on the Marketo side.