I was the backend developer on a project where the marketing team ran our email campaigns. They were using five or six separate services for it, because, in their words, none of them gave the full set of tools they needed.
I spent a weekend putting together something that ran all of those checks in one pass, and connected it to real mailboxes. It was meant to stay an internal tool. A few months of testing later it turned into this.
SpamRate sends your campaign to real mailboxes at Gmail, Outlook, Yahoo and Zoho, then reports:
• where each copy landed, including which tab, since Promotions and Updates are different problems • SPF, DKIM, DMARC, blacklists, headers and content from the same send • monitors that repeat the test and email you when placement drops
You get one test without an account, and three a day with a free one. Pro and Max add higher limits and the automated monitors. There is also a lifetime plan running until the end of summer, if paying once suits you better than a subscription: https://spamrate.is/lifetime
Worth saying plainly: seed mailboxes have no history with your domain, so this measures the filterable part rather than engagement. That's still the part you can fix before sending.
I'd like to know how you check this today, and whether anyone has found a way to notice a slide into Promotions before reply rates quietly drop.
P.S. I recently added a WordPress plugin that tests the standard WordPress emails and the WooCommerce customer emails in one click. It's been submitted to the WordPress plugin directory and is waiting on review, which takes a while. Until then it's available as a zip on the site if you want to try it.
What I liked is that the product seems to have started by reducing fragmentation rather than adding another tool to the stack.
Sometimes the biggest improvement isn't creating a new workflow—it's making an existing one coherent enough that people can actually rely on it.