I've been seeking a resolution to this problem for a bit now. We started noticing yahoo.com emails bouncing back with a deferred status last week. Here's a sample of one of the bounced messages.
3B8C812412C: to=<[redacted]@yahoo.com>, relay=none, delay=90, delays=0.05/0.02/90/0, dsn=4.4.1, status=deferred (connect to yahoo.com[18.104.22.168]:25: Connection timed out)
We're using a virtualmin setup on Ubuntu 12.04. We have no entries in dnsbl or through the mxtoolbox blacklist lookup. I've contacted the Yahoo postmaster through the bulk mail form, but that was 3 days ago and nothing has changed. All messages still bounce, but only through Yahoo.
Anyone have suggestions or help they can provide on this frustrating problem?