Email Deliverability Test: How to Check Your Cold Emails Land in the Inbox

An email deliverability test tells you where your cold emails really land, not just whether a server accepted them. Here is how to run one properly, which tools to trust for what, how to read bounce codes and Google Postmaster Tools, and what to fix when B2B emails end up in spam.

What does an email deliverability test actually measure?

It checks three separate things: whether the receiving server accepted the message, whether it reached the inbox rather than spam or Promotions, and whether your authentication and reputation signals pass. ‘Delivered’ answers only the first. A message can be accepted and still never be seen.

In cold outbound the silent failure is the dangerous one. A bounce is loud: you get a code and a reason. A spam-foldered email is accepted, produces no error and no reply, and looks exactly like a weak offer. So when replies drop, test placement before you rewrite a single line of copy. The same mailbox-provider rules apply to cold outreach and to ordinary email marketing, but cold senders have less margin for error because recipients did not ask for the message.

How do you run an email deliverability test in 15 minutes?

Send a real message from each sending mailbox to a Gmail and an Outlook account you control, open ‘Show original’ in Gmail, and confirm SPF, DKIM and DMARC all say pass. Then note whether it landed in Inbox, Promotions or Spam. Fifteen minutes catches most setup faults before a buyer sees anything.

Do it in this order:

1. Send the exact template you plan to use, in plain text, from each mailbox.
2. In Gmail, open the message, click the three-dot menu and choose Show original. Read the SPF, DKIM and DMARC lines. All three should say PASS, and the domain they pass for should be your sending domain.
3. Note the folder. Inbox, Promotions and Spam are three different outcomes.
4. Run a spam test email through a content checker such as Mail-Tester: you send a message to a generated address and it returns a score and a report.
5. Check DNS and blacklists. Google’s Admin Toolbox Check MX reads your MX and SPF records, and MXToolbox runs blacklist lookups.
6. Repeat after any DNS change, new domain or template change.

Which email deliverability tool and inbox placement test should you use?

Use layers: a manual inbox check for ground truth, a content checker, DNS and blacklist tools for setup, a seed-list inbox placement test for provider-by-provider results, Google Postmaster Tools for Gmail reputation and your bounce log. No single email deliverability tool answers everything. Each covers one blind spot.

A seed test sends your message to a panel of test mailboxes at Gmail, Outlook, Yahoo and others and reports where each one landed. GlockApps and MailReach both offer this kind of inbox placement test; check current pricing. Treat results as directional. Test mailboxes are not your buyers, and providers weigh how real recipients behave. A seed result is a smoke alarm, not a verdict, and no tool can promise inbox placement.

What does Google Postmaster Tools tell you about email deliverability in Gmail?

Google Postmaster Tools shows how Gmail sees a domain you verify: spam rate, reputation, authentication results and delivery errors. It only reports when your daily Gmail volume is high enough. Keep the spam rate under 0.30%, and ideally under 0.10%, which is Google’s recommendation.

Setup is free: add your sending domain and prove ownership with a DNS record. Google notes that data can be missing when a day’s message count is too low, to protect privacy. That matters for cold email. A domain sending about 60 emails a day, three mailboxes at roughly 20 each, may show little or nothing. Add the domain anyway, because it costs nothing and starts to help as you scale. But do not rely on it as your only alarm. For low-volume cold domains, bounce codes, your own inbox tests, seed tests and reply patterns do most of the work. For email deliverability in Gmail specifically, the spam-rate chart is the one number worth watching.

How do you read bounce codes?

A bounce carries a three-digit SMTP code and an enhanced code such as 5.1.1. Codes starting with 4 are temporary and the server may retry. Codes starting with 5 are permanent, so stop sending to that address. The enhanced code then tells you whether the fault is your list, your authentication or your sending behaviour.

These are the ones B2B senders meet most, with Gmail’s wording from Google’s SMTP error reference:

• 550 5.1.1: the account does not exist. A list problem. Remove the address and check where the list came from.
• 552 5.2.2: the recipient’s inbox is out of storage space. Treat as a dead address for cold email.
• 550 5.7.26: blocked because the sender is unauthenticated. Gmail requires SPF or DKIM. Fix DNS before you send anything else.
• 550 5.7.1, ‘likely unsolicited’: Gmail judged the message to be probably spam. Check list quality, content and recent volume.
• 421 4.7.28: Gmail saw an unusual rate of email and temporarily rate-limited it. Slow down.
• 550 5.7.515 (Outlook.com): the sending domain does not meet the required authentication level. Check SPF, DKIM and DMARC alignment.

Why do B2B emails land in spam, and what do Google, Yahoo and Microsoft now require?

Cold emails land in spam mainly because of an unverified list that produces bounces, a new domain with no sending history, sudden volume jumps, broken authentication, spam-like links and content, and recipient complaints. Since February 2024 Google and Yahoo, and since May 2025 Outlook.com, also enforce authentication and unsubscribe rules.

The published rules are specific. Google’s sender guidelines ask for SPF, DKIM and DMARC, one-click unsubscribe on marketing mail and a spam rate under 0.30%. Yahoo’s best practices say the same about the 0.3% limit, ask bulk senders to honour unsubscribes within two days and require SPF and DKIM plus DMARC. Microsoft’s Outlook.com requirements, enforced from May 5, 2025, cover domains sending over 5,000 emails a day and reject non-compliant mail. The bulk tier starts around 5,000 a day, far above a 20-per-mailbox cold setup, but Google says all senders must meet its guidelines for personal Gmail, so treat them as the floor. Our SPF, DKIM and DMARC guide covers the records.

Google Workspace mailboxes send from Google’s shared IP addresses, so the one thing left for you to damage is your own domain’s reputation. That is why we send cold email from separate domains and never from the main company domain.

When replies drop, everyone rewrites the email. Test placement first. A perfect email in the spam folder is still an email nobody read.— Murtaza Udaypurwala, DESENO

How do you fix email deliverability when cold emails land in spam?

Pause the affected mailboxes, find the cause with the tests above, fix that cause, then restart at low volume. The usual order is list first, authentication second, volume third, content last. If a sending domain is badly damaged, retiring it can be faster than nursing it back, which is why cold email never belongs on your main domain.

Use this sequence, and use the same habits to increase email deliverability before there is a problem:

1. Pause sending from the affected mailboxes so the damage stops growing.
2. Re-verify the list. Remove hard bounces and risky addresses. In one of our own list builds, addresses on catch-all domains almost never passed verification, while addresses marked valid nearly always did.
3. Confirm SPF, DKIM and DMARC pass for every mailbox.
4. Simplify the message: plain text, one link at most, no attachment, no link shorteners.
5. Cut volume and warm up again. Our setup uses about 14 days of warm-up, then roughly 20 emails per mailbox per day with 2–3 mailboxes per domain. See our email warm-up guide.
6. Retest after a few days with the 15-minute check.
7. If it will not recover, retire the domain and replace it. Bounce rate should be watched all the time, and sending should pause automatically if it spikes.

The bottom line

An email deliverability test is a habit, not an event. Test every mailbox before it sends, read the authentication results in the headers, learn the bounce codes, watch Postmaster Tools if your volume allows it, and test again after every change. Fix the list first, then authentication, volume and content. If you would rather have this handled, DESENO runs B2B email outreach for manufacturers with verified lists, separate warmed-up domains and automatic pausing.