have brought in lists from other providers who have, it seems, two issues.

(a) Poor deliverability; and
(b) poor bounce handling.

This matters because the folks in group (a) above will get your first email from us, and they won't have heard from you before in a long time. So their reaction is "huh?" and they unsubscribe. Our algorithms see high unsubscribe rates as a red flag for list quality. We're working to see how best to get them to be tolerant enough for AppSumo while not undermining our ability to detect likely abuse.

For group (b) we've seen an unexpectedly high number of hard bounces from some ISPs that should have been caught by the ESP, but weren't. That's also a significant input into our potential abuse systems. Again, we're working to smooth this out in terms of some third party ESPs.

Bottom line: Before you bring a list to FeedBlitz, scrub it of non-engaged addresses first in your current solution and remove people who've received (say) more than your ten emails and haven't opened or clicked. Just junk them, and even if that might reduce your list by a scary amount, it isn't really, because they're not interested. It will give you a much higher quality list to bring over and will avoid all of the transitional pitfalls.

Thanks!

Phil