Hi, I'm new here and wanted first to thanks everyone to make this place a very useful forum about mailing. I'm also "new" to mailing but tested and read a few things. I started a campaign for only yahoo TLD and I'm in the process of warming up ips I sent from. Did everything needed: feedbackloop, DKIM, DomainKey, SPF and RDNS. I'm using PowerMTA for sending email and doing very slow mailing for the moment (because of the warmup). I started out with 3k per day and upgraded to 5k yesterday. I have some bounce back and I manage them with software I coded. Everything goes fine except one thing. I hit sometimes greylisting and fakeMX servers. SMTP service unavailable: "421 4.7.0 [GL01] Message from (xxx.xxx.xxx.xxx) temporarily deferred - 4.16.50. Please refer to http://postmaster.yahoo.com/errors/postmaster-21.html" received from mta7.am0.yahoodns.net Will this affect my warmup process and if yes what is needed to do to correct this issue? I'm also never retry bounces in the PMTA config. Thanks in advance for all your suggestions.