I was watching my log files now looking for deferred errors, and for my surprise, we got temporary blocked by Yahoo on some SMTPs (ips), as shown:
Jan 9 13:20:52 mxcluster yahoo/smtp[8593]: 6731A13A2D956: host mta5.am0.yahoodns.net[98.136.216.25] refused to talk to me: 421 4.7.0 [TS02] Messages from X.X.X.X temporarily deferred - 4.16.56.1; see http://postmaster.yahoo.com/errors/421-ts02.html So guess what, I still have another 44k messages on active queue (a lot of them are probably to yahoo) and postfix is wasting its time and cpu trying to deliver to Yahoo when there's an active block. Yahoo suggests to try delivering in few hours, but we'll never get rid from the block if we keep trying while the block is active. This doesn't happens only with bulk senders. Many people use their hosting company to send few hundreds emails together with many other users sending legitimate mails from their mail clients… Eventually, one user will compromise all infrastructure and many people may have problem delivering their messages. There's gotta be a solution for this. - Rafael
