Email deliverability is whether a message you send actually reaches someone’s inbox, versus landing in spam or getting silently filtered before they ever see it.
For Hostinger users, that outcome depends on two separate things: whether your domain is properly authenticated through DNS, and whether the content of what you’re sending trips spam filters regardless of how clean your setup is.
Most guides on this topic only cover the first half. This one covers both, backed by real test scores rather than general advice.
To see exactly how much content alone matters once authentication is already correct, I sent two emails from the same Hostinger mailbox, seconds apart. One was a plain, ordinary message. The other was deliberately loaded with everything you’re told not to do, an all-caps subject line, “guaranteed” language, urgency phrases, a broken link.
The first scored 9 out of 10 on a deliverability test. The second scored 5.2. Same mailbox, same authentication, same domain, and the score still dropped by almost half.
That gap is what the rest of this article works through:
- What to check first on the Hostinger side
- How to measure your own score
- What actually happens when the same mail gets tested across 27 real providers rather than just one
- And what to change in your emails based on exactly what moved the numbers, not generic advice about “avoiding spam words” in the abstract
Step 1: Confirm Your DNS Authentication Is Already Correct
This has to be right before content matters at all, since a broken authentication setup can tank deliverability regardless of how careful you are with wording.
Here’s the fast version of what to check in hPanel under Emails > Domain settings:
| Record | What It Should Show |
|---|---|
| MX | mx1.hostinger.com (priority 5) and mx2.hostinger.com (priority 10) |
| SPF | A TXT record including _spf.mail.hostinger.com |
| DKIM | Either the automatic CNAME setup or a Custom DKIM record, showing as verified |
| DMARC | A TXT record starting with v=DMARC1 |
If your domain uses Hostinger’s nameservers, all four are usually already in place and marked verified without you touching anything.
If any show as missing, or your domain’s DNS is managed somewhere else entirely, our Hostinger MX records guide and email setup guide walk through the exact values and registrar-specific steps for adding them manually.
Step 2: Establish Your Baseline Score
Before you can improve anything, you need a real number to work from rather than guessing. This is genuinely the first diagnostic step, not just something I did for this article.
- Go to mail-tester.com
- It generates a unique test address, something like test-0z3ao9gpq@srv1.mail-tester.com
- Send a normal email from your Hostinger mailbox to that address, using content close to what you’d actually send
- Go back to the page and click Then check your score
Here’s what came back on my plain test email, subject line “Deliverability Test from Hostinger,” a short two-sentence body, nothing unusual:
| Check | Result |
|---|---|
| Message viewable | Passed |
| SpamAssassin | -0.5 (minor deduction) |
| Authentication (SPF/DKIM/DMARC) | Passed |
| Message quality | Flagged as improvable |
| Blocklist status | Not blocklisted |
| Broken links | -0.5 (1 broken link found) |
| Total score | 9/10 |
Even a plain, harmless message didn’t score a perfect 10, and the reason why is instructive.
The broken link penalty came from a link I’d included in a signature line that didn’t resolve. The action here is simple but easy to overlook: test every link in your signature, not just the links in your actual message body.
A stale link in a footer you copy-paste into every email costs you on every single send, quietly, without ever showing up as an obvious error.
Step 3: Test Real-World Inbox Placement Across Major Providers
A single mail-tester score tells you whether one specific inbox’s spam filter is satisfied. It doesn’t tell you what actually happens across the dozens of mail providers real recipients use.
For that, I ran a full inbox placement test, sending the same message out to test addresses across 27 different mail providers and checking where each one actually landed.
The results were a lot less clean than the 9/10 mail-tester score suggested. Out of 124 test addresses, only 82 messages were accounted for at all. Here’s the overall breakdown:
| Outcome | Percentage | Count |
|---|---|---|
| Inbox | 27% | 34 |
| Spam | 39% | 48 |
| Missing (no result within the test window) | 34% | 42 |
That means some portion of the 124 addresses in this report likely never had a message sent to them at all, rather than receiving one that then vanished or got filtered.
I can’t cleanly separate “never sent due to the recipient cap” from “sent but never arrived” within this single report, so I’m not attributing the full 34% to spam filtering or delivery failure. What the data does still support is the inbox-versus-spam split among the addresses that clearly did receive something, which is the more reliable part of this test.
Provider-by-provider, the picture varied enormously:
| Provider | Inbox | Spam | Missing |
|---|---|---|---|
| Gmail | 23% | 76% | 0% |
| Microsoft 365 | 0% | 100% | 0% |
| Outlook | 5% | 0% | 95% |
| Yahoo | 12% | 87% | 0% |
| AOL | 0% | 100% | 0% |
| Barracuda | 0% | 100% | 0% |
| iCloud | 100% | 0% | 0% |
| Mail.ru | 100% | 0% | 0% |
| GMX USA | 100% | 0% | 0% |
| Amazon WorkMail | 100% | 0% | 0% |
| Seznam | 100% | 0% | 0% |
| Centrum | 100% | 0% | 0% |
| SFR | 100% | 0% | 0% |
Gmail alone landed 76% of messages in spam in this test, and Gmail is likely where a large share of anyone’s real audience actually reads email.
Microsoft 365 and Barracuda, both common in business environments, hit 100% spam.
If your recipients are mostly on Gmail, Outlook, or a Microsoft 365 business account, a clean mail-tester score is not a reliable signal that your actual audience is receiving your mail.
A few of the smaller, more regional providers showing 100% missing (LaPoste, Free.fr, Web.de, T-Online, AT&T, Freenet, Onet) were tested against only one or two addresses each, so I wouldn’t read too much into those individually.
The pattern worth acting on is the one visible across providers with enough volume to be meaningful: Gmail, Microsoft 365, Outlook, Yahoo, AOL, and Barracuda all showed real placement problems, while iCloud, Mail.ru, and several others showed none at all on the same send.
This is exactly why the warm-up approach in Step 6 below matters more than a single good test score. Authentication and content can be perfect, and a new or unfamiliar sending domain can still land in spam at scale across the providers your actual audience uses, particularly Gmail and Microsoft 365, until you build up a real track record with each one.
Step 4: Fix the Specific Content Issues That Actually Move the Score
Testing a plain email tells you where you start. To find out what actively damages a score, I sent a second email designed to trigger every spam pattern at once: an all-caps subject line, “guaranteed” and urgency language, a suspicious link, and no plain-text version of the message.
Same mailbox, same domain, same authentication setup as the clean test above, so anything that changed came from content alone.
The score dropped to 5.2/10. Here’s the full breakdown, and the part that matters more than the total, what each line item means for how you should actually write your emails:
| SpamAssassin Rule | Penalty | What It Means | What To Do About It |
|---|---|---|---|
| GUARANTEED_100_PERCENT | -2.699 | The phrase “100% guaranteed” alone, by far the largest single deduction in the entire test | Cut this exact phrase and similar absolute guarantee language entirely, especially from subject lines and opening sentences |
| HTML_MIME_NO_HTML_TAG | -0.635 | Message sent as HTML but missing a proper HTML tag structure | If you’re sending HTML email, make sure it’s built correctly rather than just formatted text pretending to be HTML |
| SUBJ_ALL_CAPS | -0.5 | Subject line written entirely in capital letters | Never write a full subject line in caps, even for genuine urgency, use normal sentence case instead |
| 2 broken links | -1 (combined) | Both links in the message failed to resolve | Test every link before sending, the same lesson from the clean test, just compounded here |
| ACT_NOW_CAPS | -0.1 | The phrase “act now” on its own, separate from the general all-caps penalty | Avoid urgency phrasing like this even in lowercase, since the pattern itself is flagged independently of capitalization |
| MIME_HTML_ONLY | -0.1 | No plain-text version included alongside the HTML version | Always include a plain-text version alongside HTML content, most email clients and filters expect both |
Three insights worth pulling out of this table, since they change how I’d actually tell you to write emails going forward:
“100% guaranteed” alone cost more than every other issue in this email combined, nearly triple the next largest penalty. If you’re writing marketing-style copy through a Hostinger mailbox, promotional language that sounds like a guarantee is the single highest-value thing to eliminate. It’s not close.
The all-caps subject line penalty is separate from all-caps phrasing anywhere else. SUBJ_ALL_CAPS fired because of the subject line alone, while ACT_NOW_CAPS fired separately for phrasing in the body. That means a shouty subject line costs you even if the rest of your email is calm and professional, so don’t assume a strong subject alone is a small thing.
Authentication passed cleanly in both tests. This is the finding that should change how you troubleshoot a low score. If your SPF, DKIM, and DMARC are already verified, as confirmed in Step 1, and your score is still low, the problem is not your DNS. Stop checking DNS records repeatedly and start rewriting the actual message content instead.
How to Improve Inbox Placement and Avoid Spam
Setting up SPF, DKIM, and DMARC correctly, avoiding spam-triggering content, and maintaining healthy contact lists can help Hostinger emails reach the inbox more consistently.
Step 5: Respect Hostinger’s Sending Limits Before You Scale Anything Up
Improving your score doesn’t help if you can’t actually send to everyone you’re trying to reach. While testing deliverability tools, I ran into a limit worth flagging directly.
That matches the 100-recipients-per-message cap covered in our Hostinger SMTP settings guide, and it applies regardless of which plan you’re on.
Step 6: Warm Up a New Mailbox Instead of Sending in Volume Immediately
A good score on a test email doesn’t mean a brand-new domain can immediately send in volume without consequences.
I asked Hostinger’s Kodee AI assistant directly what deliverability tools or warm-up guidance Hostinger provides, since nothing in hPanel’s regular email interface surfaces a sender reputation dashboard on its own.
Regular Business Email, the mailbox product most of this article covers, doesn’t include that dashboard. It’s built around mailbox setup and sending status rather than an ongoing reputation score.
For warming up a new mailbox or domain before sending real volume, here’s the gradual approach Kodee recommends, and the reasoning behind each stage:
- Week 1: Send only to a small group of people who already trust you, and ask them to actually open the message, reply, star it, or mark it “not spam” if it lands there. These actions signal genuine engagement to receiving mail providers, which matters more at this stage than volume.
- Week 2: Increase volume slowly rather than jumping straight to your full sending list. A sudden jump looks statistically similar to spam behavior even if every message is legitimate.
- Week 3 and beyond: Scale up carefully, prioritizing your most engaged contacts first rather than blasting a full list all at once. Engagement history at this point starts working in your favor.
Putting It Together: What Actually Improves Hostinger Email Deliverability
Pulling every finding above into one place, here’s the order I’d actually work through this if I were fixing a real deliverability problem:
- Verify MX, SPF, DKIM, and DMARC are all showing verified in hPanel
- Run a baseline test on an email you’d actually send, not a placeholder
- Run a real-world inbox placement test across major providers, not just a single mail-tester score, since results vary enormously by provider
- Test every link in your message and your signature before sending anything
- Remove absolute guarantee language, “100% guaranteed” and similar phrasing, especially from subject lines
- Write subject lines in normal case, never fully capitalized
- Include a plain-text version alongside any HTML email
- Keep sends under the 100-recipient cap, or move to a dedicated tool if you’re regularly exceeding it
- If the domain or mailbox is new, warm it up gradually over two to three weeks rather than sending in volume immediately, especially with Gmail and Microsoft 365 recipients
Troubleshooting Common Deliverability Issues
- Score is low despite correct SPF, DKIM, and DMARC. Authentication and content are graded separately. Run a fresh mail-tester check and read the SpamAssassin breakdown closely, since the issue is almost certainly in the message itself, not your DNS.
- A good mail-tester score, but mail still isn’t reaching people. A single test score doesn’t reflect real-world placement across providers. Run a broader inbox placement test (using a tool like EasyDMARC), since Gmail, Microsoft 365, and similar large providers can still route mail to spam even when a single spam-filter test scores well.
- “Too many recipients” error when sending. You’ve hit the 100-recipient-per-message cap that applies across every Hostinger email plan. Split large sends into smaller batches or use a dedicated email marketing tool instead.
- New domain’s mail keeps landing in spam despite clean content. This is often a reputation problem rather than a configuration one. Follow a gradual warm-up approach rather than sending in volume immediately on a brand-new domain.
- Broken link penalties on a test score. Double check every link in your signature and footer, not just the main message content, since a stale signature link costs the same as one in the body and is easy to miss.
- Unsure whether Hostinger offers deliverability monitoring. Regular Hostinger email hosting doesn’t include a reputation dashboard. That functionality lives in Hostinger Reach, a separate marketing product, if ongoing deliverability monitoring is something you need.
