You set up your email in HubSpot, put your company domain in the "From" address, and started sending. Looks right in the UI. But if you've never configured a custom sending domain, your emails are leaving HubSpot authenticated as HubSpot, not as you. Gmail, Outlook, and every major inbox provider can see the difference.
Here's what's happening and how to fix it.
The gap between "From" and "Sent via"
When someone receives your email, their inbox provider checks more than the "From" name they see. It checks the Return-Path header (where bounces go) and the DKIM signature domain (who cryptographically signed the message). Without a custom sending domain, both of those point to HubSpot's infrastructure, not your domain.
This creates an alignment failure. Your DMARC policy is set up for your domain. Your DKIM signature is from HubSpot's domain. They don't match, and that mismatch degrades your deliverability, sometimes dramatically.
Gmail has been enforcing stricter alignment since early 2024. If you're sending more than 5,000 emails a day to Gmail addresses without proper DKIM and DMARC alignment, you're already losing inbox placement.
How to check if this applies to you
Open any HubSpot marketing email in your Gmail inbox (your own test). Click the three-dot menu and select "Show original." Look for:
- Return-Path: If it shows something ending in
@hubspotemail.netor@mta.hubspotemail.net, you have not configured a custom sending domain. - DKIM-Signature d= If the domain after
d=is not your domain, your DKIM is not aligned.
If either applies, your emails are being delivered on HubSpot's sending reputation, not yours.
The fix
In HubSpot: Settings > Content > Domains & URLs > Connect a domain > Email Sending. Add your sending domain (typically mail.yourdomain.com or hs.yourdomain.com), then follow the DNS record steps. HubSpot will give you CNAME and DKIM records to add in your DNS provider. Once verified, set that domain as your default sending domain.
Adding a custom sending domain is the single highest-impact email deliverability improvement most HubSpot portals have never made.
After you do it, also confirm your domain has a DMARC record published. If it doesn't, add one. A p=none policy is a starting point. Once you've confirmed alignment, move to p=quarantine and eventually p=reject.
What this costs you if you skip it
Every email you send without proper alignment is training inbox providers to treat your domain as a lower-trust sender. That reputation damage compounds. Getting it back takes months of consistent, clean sending, and you can't begin that recovery until the sending domain is fixed.
