Let us take a moment to talk about SMTP status codes. Specifically, the kind that start with the number 4. Say you've just sent out your latest email, whether it be a newsletter or marketing…
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Here's one I hadn't seen before. A sender was hitting this deferral when trying to deliver mail to Microsoft (Hotmail/Outlook.com) domains: smtp;451 4.7.652 The mail serv…
Time for another Tuesday Tip here on Spam Resource. Tuesday Tips are meant to be short little bits of wisdom, easily digestible deliverability knowledge nuggets. Today's to…
Gmail has very recently unveiled a series of new deferral/rejection messages. You may want to familiarize yourself with the following new SMTP responses: 421 4.7.28 Our system ha…
