When a mailbox provider rejects or defers an email it sends back a message explaining why. Those messages begin with a three digit number (starting with a “5” for rejections and a “4” for deferrals), followed by text that explains why the mail wasn’t accepted. That text often contains a link to follow for more information, or a mailbox provider specific code you can...
The nice folks over at Postmark shared a new deliverability resource last week. The SMTP Field Manual. This is a collection of SMTP responses they’ve seen in the wild. This is a useful resource. They’re also collecting responses from other senders, meaning we can crowdsource a useful resource for email deliverability folks.
At least one ESP and Spamhaus are currently investigating bounce messages at a couple ISPs incorrectly pointing to Spamhaus as the reason for the block. The bounce messages are taking the form: smtp; 554 p3plibsmtp03-07.prod.phx3.secureserver.net bizsmtp IB105. Connection refused. 192.0.2.24 is listed on the Exploits Block List (XBL) <; Please visit for more information. smtp; 553 5.7.1 [BL21]...
RSS - Posts