I have the Sparkpost extension working great, but after 3 months of weekly mailings, 225 of my 2000 mailing list contacts have been marked "On Hold." This is a much higher attrition rate than with our old Mailchimp setup.
The Suppression list in Sparkpost only has 25 addresses in it. The other 200 seem to have been set to "On Hold" by the extension because of block bounces - cases where the recipient mail server automatically deemed our email unworthy of delivery, but the actual recipient never asked to be unsubscribed.
I don't want block bounces to permanently remove someone from our mailings. I could use the Sparkpost suppression list to remove our contacts who have actually opted out (marked our email as spam, or clicked the Unsubscribe header in their email client). Then I could re-enable all the other "On Hold" addresses. But it seems tedious to have to do this every month or so.
I found the logic in the extension code where block bounces immediately trigger "On Hold" status, but it's mixed up with enough other bounce cases that it doesn't seem trivial to change how block bounces are handled.
Has anyone else encountered this? Has anyone found a solution, or have any ideas? Thanks!