Spam Resource: All Things Deliverability

As of July 3, 2025, Cloudflare is enforcing a new requirement for its Email Routing platform: Messages must be authenticated with either SPF or DKIM in order to be forwarded. No…

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…

Way back in 2020, I shared with you " The Ultimate SPAM Cookbook " and a lovely review of it (with a few recipes) from Miriam Di Nunzio of the Chicago Sun-Times , and s…

As of June 4, 2025, Let's Encrypt has stopped sending out email reminders for upcoming TLS certificate expirations. They publicly announced the change in late June to make s…

The Wall Street Journal recently ran a piece warning readers not to click unsubscribe links in emails . The idea is that these links are sometimes traps used by bad actors to har…

Allow me to waste just a tiny little bit of blog space today to help you answer a question that you were probably afraid to ask: How do you pronounce the terms DKIM and DMARC? L…

Just about weekly, somebody reaches out to me with something like this: Help! Our email marketing campaigns are going to the spam folder. I read your advice, so I've implemen…

Yahoo Mail has long been the webmail destination for mail sent to the AT&T consumer mailbox domains. Meaning that if you had an AT&T email account, you used Yahoo Mail to…

Yahoo Mail is trying to help the inbox-overwhelmed crowd get back on top of unread piles with a new mobile feature called Catch Up . This AI-powered tool is live now in the Yahoo…

Microsoft recently joined the "top four" mailbox providers (aka "MAGY," Microsoft, Apple, Google, and Yahoo) with updated authentication and email hygiene sta…

Here's a quick reminder for anyone building their own email messages: Gmail wants your Message-ID header to be properly formatted, which means that the message-ID value must …

Reputation is an oft-used term in the realm of sending email. We encourage those sending email marketing, newsletters, or other legitimate emails to have a good sending reputatio…

Swaks has long been my favorite quick and dirty tool for poking at mail servers. It's powerful, flexible, scriptable, and it doesn't hide anything behind a shiny GUI. I f…

Google recently updated its email sender guidelines with clearer instructions on what not to do when it comes to your sender name (the friendly from) and your subject line. The …

I sometimes call a re-engagement campaign a "winback" campaign because the goal is simple: try to "win back" a subscriber, meaning to keep them active in your…