I have noticed that in the past, after an email account was warmed up we just started sending 30 email in the campaign. I used to always get flagged for blacklist after that. I started a ramp-up sequence now and it works much better. After warmup, 3 to 4 weeks, I only send 5 email in a campaign per day for the first week, then I ramp it up to 10 per day for the next week, then 15 per day for the next, all the way up to 25 emails a day. Once I started doing this, I no longer was being blacklisted. I think it would be nice if you create a Campaign ramp-up that does this automatically for us.