The best email deliverability tools, and how to test before you send

The short answer: how to tell if email goes to spam

For a quick check of one email, use Mail-Tester: send it a real copy of your newsletter or site email, and it scores the message out of 10 and reports on its authentication, blacklists and content, free for three tests a day. For your domain's records, use MxToolbox, whose free lookups show your SPF, DKIM and DMARC records and check a sending IP against more than 100 blacklists. For where the email lands, use GlockApps' free spam checker, which needs no account and shows whether it reached the inbox, a tab or spam at Gmail, Outlook, Yahoo and AOL.

Once you send to a real list, reports take over from tests. For Gmail's own figures, use Google Postmaster Tools, which needs only a Google account and a DNS record and shows the user-reported spam rate that Google's sender rules are measured against. For DMARC reports, which list every service sending mail as your domain, the no-cost choices are Postmark's weekly email digest, Valimail Monitor and a free GlockApps account, which covers 10,000 DMARC messages a month. The free plan at dmarcian is for personal, non-business domains only. None of the basic checks requires a paid plan.

What SPF, DKIM and DMARC results mean in plain words

Most tools here report the same three checks. SPF is a list, published in your domain's DNS, of the services allowed to send mail as you, and Google's sender guidelines say it should include every one of them: for a creator, often the newsletter platform, the shop and whatever sends receipts. DKIM is a signature on each message that receiving servers check against a public key, to confirm the domain owner really sent it. DMARC is a third record telling receiving servers what to do with mail that does not pass SPF or DKIM, and Google's DMARC setup guide lists the options as reject, quarantine or deliver.

A DMARC pass needs one more thing, which Google calls alignment. The message must pass SPF or DKIM, and the domain that passed must match the domain in the From address or, under the default relaxed setting, share its main domain, as send.yourdomain.com does with yourdomain.com. That is why a test can show SPF passing and DMARC failing: the platform's own domain passed, not yours. The fix is normally the domain-authentication step in the platform's settings, and the newsletter setup guide covers what each record does.

To check a single message, Google's help page on authenticated messages says to open it in Gmail on a computer and click the Down arrow below the sender's name. A Mailed by line with a domain name and a Signed by line with the sending domain mean the message is authenticated, and a question mark next to the sender's name means it is not. On your own sends, Signed by should show your domain: that is the DKIM signature DMARC can match to your From address.

A spam score is not inbox placement: what each test proves

The tools fall into four kinds, and each answers a different question. A spam-score test such as Mail-Tester runs your message through SpamAssassin, an open-source filter, and checks your setup. Mail-Tester's own FAQ states the limit: all spam filters work differently, so a message that passes there might not pass in your own office inbox. It also warns that more email is blocked outright than caught by spam filters, and that mail reaching neither the inbox nor spam most probably comes from a blacklisted server.

An inbox placement test, also called a seed test, sends your email to a set of test mailboxes at real providers and reports where each copy landed. That is closer to what readers see, but it is still a sample of test accounts rather than your list. Real engagement matters too: Google's own deliverability analysis gives recommendations when recipients indicate they did not open or interact with your email.

Mailbox provider dashboards such as Google Postmaster Tools report what actually happened at Gmail, but only for personal Gmail addresses and only on days with enough volume. DMARC reports answer a fourth question: which services send mail as your domain, and whether each one passes. They are a record of authentication, not of which folder a message reached.

So treat a clean score as a starting point rather than a promise. Google's help page on authentication says that because spammers can also authenticate mail, authentication by itself does not guarantee delivery.

Mail-Tester: a free score out of 10, three tests a day

Mail-Tester needs no account for occasional tests, only one email. Its FAQ describes the process: the site gives you a random address, you send a message to it from your newsletter platform or mail app, then click Check your score, and it analyses the message, your mail server and your sending IP. Mail-Tester's API documentation lists what the result page covers: each notable SpamAssassin rule with its score, authentication tests including SPF and DKIM, checks on the HTML, every blacklist tested and any broken links.

The trade-offs are the daily limit and privacy. Free use allows three tests in any 24 hours. The FAQ says results stay visible for seven days to anyone who has the exact test address, or 30 days with an account and your own test prefix, so do not test a message carrying private links or codes. Monthly plans start at $10 for 50 tests, plus VAT, and the pricing page also lists one-time packs from $5 for 10 tests. An account adds usage statistics and a list of every test from the last 30 days, and the FAQ says the JSON API comes with the paid plans.

MxToolbox: free DNS and blacklist lookups for your domain

MxToolbox answers a narrower question, whether your DNS records and sending IP look right, and most of its checks need no email at all. Its SuperTool runs SPF, DKIM, DMARC, MX and other lookups from one search box, and its blacklist check tests a mail server's IP address against more than 100 DNS-based blacklists, which MxToolbox describes as a common way of reducing spam. If you do not know which IP your platform sends from, its Email Deliverability tool works the other way round. Send any email to the address on that page, and it replies with a link to a report on your headers, your outbound IP's blacklist reputation and your SPF records.

The free tier has limits. MxToolbox's Email Health page allows free users one report every 24 hours, a broader scan of your mail server, web server, DNS and blacklists. A free account includes one blacklist monitor, checked weekly against the top 30 blacklists. Paid monitoring starts with Delivery Center at $129 a month, which adds 30 inbox placement analyses a month, DMARC reporting and up to five domains.

GlockApps: a free look at where your email actually lands

GlockApps is built around inbox placement testing. Its free spam checker needs no account: you send an email of up to 10 MB to the address it shows. It then reports whether the message landed in the inbox, a tab or spam or went missing, along with a SpamAssassin score, a blacklist check on your sending IP and SPF, DKIM and DMARC results. GlockApps says the free checker covers Gmail, Yahoo, AOL and Outlook.

A free account adds two full Inbox Insight tests with no card required. You paste an ID string into the email and send it to GlockApps' seed list, a set of mailboxes it manages at providers its spam testing page lists from Gmail and Outlook to GMX, Web.de and Naver. GlockApps says Inbox Insight can test against five filters: SpamAssassin, Barracuda, Microsoft Exchange Online Protection, Proofpoint and what it calls an exclusive Google filter. You choose which filters and providers each test uses. The same free account includes DMARC Analytics for 10,000 DMARC messages a month across unlimited domains.

The catch is the paid step. The Essential bundle costs $85 a month billed monthly for 30 spam test credits a month, or $59 a month billed yearly, which is $708 a year for 360 credits. If you only test before launches, a one-off pack of three credits costs $16.99 and lasts one month. Beyond the free DMARC allowance, DMARC Analytics Essential is $55 a month for 1,000,000 messages.

Google Postmaster Tools: Gmail's own numbers for your domain

Google Postmaster Tools is the only tool here that reports what Gmail itself recorded. Google's setup page says you need a Google account, then you add the domain you sign mail with, either the domain in your DKIM signature or your SPF Return-Path domain, and copy a TXT or CNAME record into your DNS. The data covers mail to personal Gmail addresses only, those ending in gmail.com or googlemail.com, and the dashboards cover spam rate, authentication and delivery errors, plus a Compliance status dashboard that checks you against Gmail's sender requirements.

The spam rate is the number to watch. Google's sender guidelines require every sender to keep the rate reported in Postmaster Tools below 0.3 percent. Google's dashboards page defines the rate as the share of DKIM-authenticated messages delivered to an engaged recipient's inbox that the recipient then marks as spam. Google adds that if Gmail sends many of your messages to spam by itself, the rate can look low, because fewer of them reach the inbox.

Two details matter. The setup page says data can be missing when a day's volume is too low, to protect users' privacy, so a small list may see gaps. And Google says the Domain and IP Reputation dashboards from the old interface will be retired, so do not build a routine on them. Microsoft's nearest equivalent, SNDS, reports by IP address, and access is for the IPs you are responsible for, so it helps only if you control the sending IPs.

Postmark's free DMARC digest: one email a week, no dashboard

DMARC reports come from the mailbox providers themselves, and Google's DMARC setup guide warns that a domain can receive many reports every day. A report tool reads them for you. Postmark's free DMARC monitoring, run by an email service for web apps, takes one DNS record. You enter your email address and domain and publish the record it gives you, which sets the policy to none (p=none) and addresses reports to Postmark. Postmark then turns the reports from major mailbox providers into a human-readable email every Monday morning. It says verifying the record can take up to 24 hours. If your domain already has a DMARC record, keep its policy and add Postmark's report address to the existing list of report addresses (the rua tag) rather than replacing it. Google's guide shows one record sending reports to two addresses.

The free digest covers your top 10 mail sources with five IP addresses each and seven days of report history, by email only, which shows which services send as your domain, such as a shop or a form tool you had forgotten. The paid version, DMARC Digests, costs $14 a month per domain after a 14-day free trial and adds every source and IP, 60 days of history and a web dashboard.

Valimail and dmarcian: free dashboards, one for personal use

Valimail Monitor is a free DMARC dashboard, which its Monitor page says comes with no trial offers, credit cards or obligations. It names the services sending from your domain instead of leaving you with raw IP addresses, shows where you are passing and failing DMARC, and checks whether you are ready for Google, Microsoft and Yahoo's DKIM, SPF and DMARC requirements. Valimail says Monitor helps you identify 100 percent of the services sending from your domains. The trade-offs: its pricing and Monitor pages list no usage limits for the free plan, and Enforce, the product that automates DMARC tasks, is priced on request, as is the logo product Amplify.

The free Personal plan at dmarcian allows up to two domains, 1,250 DMARC-capable messages a month and one month of history, but dmarcian limits it to non-business domains, such as family photos or hobbies. Its pricing page says the software regularly audits Personal plans, and an account containing a domain associated with a business expires, with the option to move to a paid plan without losing data. If your newsletter is part of a business, plan on Basic: $24 a month billed monthly, or $19.99 a month billed yearly, before tax. It covers up to two domains, 100,000 messages a month and three months of history, and its 30-day trial needs no card.

A routine before a launch, using only free tools

Run this a week before a launch, a sponsor send or a move to a new platform, and again on the day.

1. Check the records. Look up your domain's SPF, DKIM and DMARC records with MxToolbox, and confirm every service that sends as you, from the newsletter platform to the shop, is in your SPF record or signs with DKIM for your domain.

2. Test the real email. Send the actual issue, from the platform and From address you will use on the day, to Mail-Tester, fix every failed check, then test again.

3. Check placement. Send the same email to GlockApps' free spam checker, or use a free full test, and note any provider where it lands in spam or goes missing.

4. Check it as a reader. Send a copy to a personal Gmail account and confirm the Mailed by and Signed by lines appear, with your domain on the Signed by line.

5. Watch the days after. If Postmaster Tools has data for your domain, check the spam rate a day or two after the send, since Google says the data is typically updated within 24 hours, and read the next DMARC digest for any source that failed.

If you have just moved platforms, your sending domain may have no history with your list yet, and the Substack alternatives guide covers starting with your most recent openers and widening from there.

When a check fails, fix it in this order

Authentication comes first, because Google's sender guidelines say messages that are not authenticated might be marked as spam or rejected. An SPF or DKIM fail, or a DMARC fail while SPF passes, often means a sending service has not been set up for your domain: finish its domain-authentication step and test again. Google's DMARC guide asks you to allow 48 hours after setting up SPF or DKIM before you add DMARC.

A blacklist hit is next. If your platform sends from a shared IP address, Google's guidelines note that the activity of every sender on it affects the reputation of all of them. Report the listing to the platform's support team rather than trying to delist an address you do not control.

Content warnings come after that: Mail-Tester and GlockApps both flag HTML, image and link problems. If Postmaster Tools shows a rising spam rate, Google's advice is about the list rather than the copy: send only to people who opted in, confirm addresses before subscribing them, make unsubscribing easy and consider removing people who never open. If you meet Google's sender guidelines and believe Gmail is still misfiling your mail, a verified domain owner can file a report through Report delivery issue in Postmaster Tools.

A clean inbox matters most when a clip takes off

For video creators, the biggest sends often follow a spike that started on Shorts, Reels or TikTok: a launch, a sponsor issue or a welcome email to hundreds of new subscribers at once. That is when a spam folder costs the most, because new subscribers have no history with your mail and may never think to look for it. Run the routine before those sends, not after. FrameOS handles the step where that spike starts, turning a long recording into captioned vertical clips. For when and how to ask viewers to subscribe, see how to turn viewers into subscribers.