HubSpot has no API behind its "Send test email" button, so this is the one test where you press a button in HubSpot yourself. It is worth it: the email that arrives carries what a copy pasted into another tool never does, HubSpot's sending servers, the DKIM signature of your connected domain (or of HubSpot's own, if it is not connected yet) and the tracking HubSpot writes into your links.
How a test works
Connect your account above and press Test next to an email. The page reserves a test address, and when the folder check is on, it also picks the provider inboxes and makes a copy of your email whose subject ends with a short marker, because that marker is how those inboxes recognise the test. You open the copy in HubSpot (or the email itself, when the folder check is off), paste the list of addresses into Send test email and send. Your original email is never edited, and once the page sees the test arrive it deletes the copy and links to the report.
There is one API that sends a marketing email, HubSpot's single-send. This app does not use it, because it needs Marketing Hub Enterprise and turns every recipient into a marketing contact you pay for, about thirty of them per test.
The report is the same one the site gives: a score out of 100 and the classic one out of 10, SPF, DKIM and DMARC with alignment, reverse DNS, 21 blocklists, links and HTML, Gmail's and Yahoo's rules for bulk senders, and a written plan with the DNS records to add. If DKIM is signed by a HubSpot domain rather than yours, your sending domain is not connected yet, and HubSpot gives you the records for it when you connect the domain in its settings.
With the folder check, the test also reaches mailboxes at Gmail, Outlook, Yahoo and other providers, and over the next half hour the report fills in whether each one put it in the inbox, in promotions or in spam. The Gmail ones are public test mailboxes, where anyone can see the subject, the sender name and the folder, so leave the box unticked for anything confidential.
History
Every test you run from this page stays in a list with both scores, the folder counts and a small chart of the score. Each row names the checks that changed since the test before it, so after you connect a sending domain the next test says DKIM went from fail to pass.
A contact that checks every email
One test covers one email. To keep an eye on everything after it, add a permanent address for your sending domain. It appears in your HubSpot as a single contact named Email Spam Tester, and the page can put it into any of your static lists; an active list picks it up when the contact matches the list's filters. Each email that contact receives gets the full check, and they line up here as a series, with the problems that keep repeating.
If your account uses marketing contacts, set this one as marketing, or HubSpot will not send it marketing email. It is one contact and counts like any other. Stop removes it again, and so does disconnecting.
What the connection allows
The app asks HubSpot for six scopes. Marketing email access is for listing your emails and for the test copy: making it, putting the marker in its subject, deleting it. Contact access covers the one contact holding our address, and list access is for showing your lists and adding that contact to the static ones you pick. The last, oauth, only tells the app which account connected. Nothing here sends email or edits the emails you wrote, and the app reads no other contacts.
The tokens are stored encrypted. Disconnect on this page and the app deletes its contact, revokes its access at HubSpot (that uninstalls the app) and signs out every browser. What is stored and for how long is in the privacy policy.
Price
Free to use right now, like the rest of Email Spam Tester. The source of the HubSpot app's configuration is on GitHub.