Top reasons emails get marked as spam #

Emails being marked as spam usually happens because of one (or more) of these:

• Domain blacklist: your domain has a poor reputation or was flagged.
• IP blacklist: the sending server IP is listed on an RBL/DNSBL (common on shared hosting).
• Missing authentication: recipient providers want SPF/DKIM (and increasingly DMARC).
• Recipient-side filters: the recipient’s mail host applies custom rules based on content/attachments.
• Bad sending method: website forms/apps sending in a way that looks suspicious (or unauthenticated).
• Content + engagement: spammy wording, too many links, or recipients ignore/mark messages as spam.

Fix 1: Check if your domain is blacklisted #

If your domain is on a blacklist, some providers will automatically route your emails to spam (or reject them).
Brixly specifically calls out domain blacklisting as a common cause.

1. Run a blacklist check (domain + mail server).
2. If listed, identify what triggered it (compromised account, spammy campaigns, hacked form, etc.).
3. Fix the root cause first, then request delisting where applicable.

Helpful tool:
MXToolbox (MX + blacklist diagnostics).

Fix 2: Check if your sending IP is blacklisted #

If the server IP is blacklisted, receiving providers may mark your email as spam. This is a known shared-hosting issue because multiple users share the same IP.

Use an IP blocklist check:
MXToolbox IP Blacklist Check.

Fix 3: Publish SPF, DKIM, and DMARC #

Some recipient mail hosts require additional validation like SPF or DKIM.
Google states senders should set up SPF or DKIM (and bulk senders must use SPF, DKIM, and DMARC).
Microsoft also recommends SPF alongside DKIM and DMARC as part of an overall authentication strategy.

• SPF authorizes which servers can send mail for your domain (standardized in RFC 7208).
• DKIM signs outgoing emails so recipients can verify integrity and legitimacy.
• DMARC tells receivers what to do when SPF/DKIM fail and provides reporting (RFC 7489).

Official references:
Google email sender guidelines
|
Microsoft SPF configuration guidance
|
RFC 7489 (DMARC)

Fix 4: Stop sending from unsafe methods (forms/apps) #

One of the fastest ways to get flagged is sending from scripts or applications in a way that looks unauthenticated.
For example, many PHP apps default to sending mail in ways that can cause deliverability issues and spam placement.

• Contact forms: configure SMTP authentication (don’t rely on weak defaults).
• WordPress: use SMTP plugins configured with your mailbox (or a dedicated transactional provider).
• Apps/CRMs: ensure the sender domain matches authenticated sending sources (SPF/DKIM alignment matters).

Fix 5: Clean up subject/body content #

Even with perfect authentication, spammy content can still trigger filters—especially if the recipient has custom anti-spam rules.

Quick “looks like spam” checklist #

• Too many links (especially shortened URLs)
• ALL CAPS and excessive punctuation!!!
• Overly salesy words (“FREE”, “GUARANTEED”, “ACT NOW”)
• Image-only emails with little text
• Attachments in first-time emails (some providers treat this as risky)

Fast test #

1. Send a plain-text version of the same email.
2. If it lands in inbox, your HTML formatting/signature is the culprit.
3. Rebuild the email with simpler formatting and fewer links.

Fix 6: Improve list quality and engagement #

If you send to old lists, purchased emails, or invalid addresses, you’ll generate bounces and complaints. That kills reputation fast.
Clean lists and consistent engagement reduce spam placement over time.

• Remove hard bounces immediately
• Avoid purchased lists (high complaint risk)
• Warm up sending volume gradually (don’t jump from 0 to 2,000/day overnight)
• Ask recipients to “Not spam” / add you to contacts if it’s a relationship-based email flow

Fix 7: Diagnose using email headers #

If you’re still not sure why messages are being marked as spam, ask the recipient for the email headers.
Headers can show authentication results and routing details. Brixly specifically recommends collecting headers plus sender/recipient/subject/date-time for support diagnosis.

Fix 8: Test your email score (Mail-Tester + Spam Checker) #

Testing tools can quickly point out missing authentication, blacklist problems, and spammy content patterns.
Brixly recommends using Mail-Tester or Experte’s Spam Checker to diagnose issues.

Mail-Tester (spam score + auth checks) #

1. Open Mail-Tester and copy the generated test email address.
2. Send a real test message with normal content to that address.
3. Return to Mail-Tester and check your score/report.

Tool link:
Mail-Tester.

Experte Spam Checker (content + placement hints) #

Tool link:
Experte Spam Checker.

Fix 9: When to contact Hosticko Support #

If you’ve done the checks above and your emails are still being marked as spam, open a ticket and include:

• Sender email address
• Recipient email address
• Subject line + date/time sent (with timezone)
• Email headers (from recipient)
• Whether you sent from Outlook/Webmail/website form/app
• Any Mail-Tester/Experte results (copy/paste key findings)

Submit here:
https://client.hosticko.com/submitticket.php

Related Hosticko guides #

• 550 Message Classified as Spam Error (Fix)
• 550 Please Turn On SMTP Authentication (Fix)
• Correct SPF Record for Hosticko Hosting
• Email Sending Limits

Replace internal links with your actual Hosticko knowledgebase URLs if they differ.

FAQs #

Can shared hosting cause emails to go to spam? #

Yes. If the sending IP is shared and gets blacklisted, other users on that IP can be affected.

Do I really need DMARC? #

If you send any meaningful volume (or want strong protection), yes. DMARC lets domain owners publish policies for handling failed authentication (and receive reports).

Why do my emails land in spam only at certain providers? #

Each provider uses different reputation data and filtering rules, and some apply stricter authentication requirements than others.