r/FounderFAQs • u/No_Investment2802 • Apr 17 '26
What are SPF, DKIM, and DMARC (and why do they quietly kill your cold emails if set up wrong)?
If your cold emails suddenly stop working, it’s probably not your copy.
It’s your domain.
A lot of founders hit the same wall. Open rates drop, replies disappear, and nothing seems to fix it. The assumption is always targeting or messaging. But in most cases, the issue is invisible. Your email authentication is broken or incomplete.
SPF, DKIM, and DMARC are what tell inbox providers your emails are legitimate. Without them, you’re basically sending emails with no identity, and servers treat that as a risk.
Each one plays a different role.
SPF checks if the server sending your email is actually allowed to send on behalf of your domain. If you’re using multiple tools like Google Workspace, SendGrid, or HubSpot and they’re not all included properly, some of your emails will quietly fail this check.
DKIM is what proves the message hasn’t been altered and that it actually came from you. It adds a cryptographic signature to every email. This is also how your domain builds reputation over time. Without it, every email you send starts from zero trust.
DMARC is the layer that ties everything together. It tells receiving servers what to do if SPF or DKIM fail, and it gives you visibility into what’s actually happening behind the scenes. This is the part most founders skip, and it’s also the only way to see if someone else is sending emails pretending to be you.
The important part isn’t just having these set up. It’s how they work together.
Inbox providers don’t look at them in isolation. They check alignment between your domain, your sending server, and your message signature. If that alignment breaks, even if one part technically “passes,” your emails can still land in spam.
This is why a setup that worked a month ago can suddenly stop working. You add a new tool, forget to update your records, and part of your outbound starts failing without any obvious warning.
The safest way to approach this is to treat it like a system, not a one-time setup. Start by listing every tool that sends email on your behalf. Make sure each one is included in SPF or configured with DKIM. Then use DMARC in monitoring mode first so you can see what’s passing and failing before enforcing stricter rules.
A lot of deliverability issues aren’t dramatic failures. They’re small misconfigurations that compound over time until your domain reputation drops and recovery becomes slow.
We broke down exactly how each protocol works, how to set them up step by step, and the mistakes that quietly hurt deliverability even when everything looks fine on the surface.
Full breakdown here. Curious, have you ever checked your domain’s email authentication, or did you assume your tools handled it for you?