Why Your Emails Are in Spam: 9 Deliverability Problems Senders Ignore (2026)

You spent hours crafting your copy and testing all the links, then hit send. A week later, open rates are stagnant and you hear that your email went straight into your customer's junk folder. You didn't see anything wrong on your dashboard, and your email platform reports all of your emails as delivered.

Delivered means that the receiver accepted the email. It doesn't mean that it went into the inbox. The filters of Gmail, Yahoo, and Outlook decide that based on dozens of criteria about you as a sender.

These filters are getting stricter. Google and Yahoo started implementing mandatory sender requirements in 2024, and Microsoft followed with Outlook.com in May 2025. In November 2025, Gmail ramped up enforcement, including rejection of non-compliant emails. However, plenty of companies still aren't aware of these changes.

Below are nine criteria that silently send legitimate email to spam, and how to solve each one.

1. Your SPF and DKIM Pass, but DMARC Fails Anyway

SPF and DKIM should be passed to get emails delivered reliably. This is common knowledge among marketers. What is often missed here is that passing SPF and DKIM doesn't mean passing the DMARC test.

DMARC checks for the alignment of your domain name (the one you put in the "From" field) with the SPF and/or DKIM domain (the d= attribute in the DKIM signature or the Return-Path for SPF).

If your newsletter service uses SPF, which includes its own Return-Path, and DKIM, which uses its own domain in the d= attribute, you can have both SPF and DKIM passed and DMARC failed. This is because none of the domains are the same as yours.

To solve the problem, configure your DKIM record and a custom return path through your email provider. The path and the signing domain should belong to you or be your subdomain. Then check DMARC aggregate reports (they should be sent to the rua email in your record) for several weeks.

2. Your SPF Record Is Too Long

As your marketing evolves, you add different services: newsletter, social media management, support desk, etc. Each of these services wants you to include it in your SPF record.

This record, however, has a limit of DNS lookups: only 10. Passing this limit leads to a permanent error, which receivers treat as a failure. The thing is, many services don't care about this limit, and many teams don't pay attention to it either. An SPF checker will do it for you instantly, though.

Check your SPF record every three months. Remove services that you no longer use and, if possible, move the services that send out a lot of emails to a new subdomain with a separate SPF record.

3. You Reached the Bulk Sender Criteria Without Realizing It

Google, Microsoft, and Yahoo treat you as a bulk sender if you send 5,000 emails or more a day to their users. This threshold can easily be crossed with one large promotion or order confirmation mailing, and Google will keep treating you as a bulk sender after that.

Above this threshold, there are additional requirements:

• You should pass SPF and DKIM and have a DMARC policy published (p=none is enough, as long as it is aligned with your From domain).
• There should be an unsubscribe option in marketing messages (both List-Unsubscribe and List-Unsubscribe-Post headers), and Gmail requires requests to be processed within two days.
• Your complaint rate shouldn't exceed 0.3% (0.1% is better).
• Outlook can reject non-compliant mailings with a 550 5.7.515 error and won't allow you to escape this rule by putting yourself on their "Safe Senders" list.

4. The IP Address That Sends Your Email Has a Reputation of Its Own

Emails are sent to mailbox providers by specific IP addresses. On a shared IP, you'll inherit the reputation of everyone using it; on a dedicated IP, your reputation is formed with all the past mistakes included.

First, check the IP address you use to send your emails. You can find it in the Received headers of a message that went to spam. After that, run the address through an IP lookup tool to discover its location and who owns and hosts it.

You may be surprised to learn that your emails pass through a cheap cloud service with a poor reputation or a server in a country where you don't have clients. Either one can raise flags with filters.

After you learn whose IP address you use, check whether it is listed on blocklists like Spamhaus, Barracuda, and SpamCop. These listings can cause many rejections. Also, ensure that this IP address has a valid reverse DNS (PTR) record that resolves to a hostname you own. Gmail requires this for every sender, regardless of volume.

5. A New Domain or a Lookalike One

Domain reputation has become as important as IP reputation. A domain that was created last month has no history and is treated as suspicious.

The same applies if you send emails not from your own domain but from a domain different from your website or similar to it. Such a pattern resembles a typical phishing scam. Send emails from your domain or from a subdomain of it, and give a newly created domain several weeks of low-volume sending to engaged contacts before large mailings.

Don't change your domain frequently. When you do, all the reputation you have is thrown away, and filters will have to check you from scratch again.

6. Outdated Addresses and Spam Traps on Your List

Email lists decay over time as people change workplaces or delete mailboxes. These outdated email addresses are dangerous: many providers recycle them into spam traps, and mailing these addresses signals poor list hygiene to the filter.

Hard bounces should be removed automatically after the first attempt. Inactive contacts (those who haven't opened or clicked your emails in 6-12 months) should be asked to confirm that they want to continue receiving your emails and removed from your list if they don't reply.

Use your re-engagement strategy carefully: Apple Mail Privacy Protection preloads images and inflates open rates with them. Clicks and replies are more trustworthy metrics.

And never buy email lists. They will contain spam traps and people who didn't opt in to receive your emails.

7. Difficulty Unsubscribing

When unsubscribing from your email list takes effort, people mark the emails as spam. Every complaint counts against you. A preference center with ten checkboxes, a login wall, or an unsubscribe link in tiny gray font all have the same effect.

To fix this:

• Place a clear unsubscribe link in the footer.
• Enable one-click unsubscribing via the List-Unsubscribe and List-Unsubscribe-Post headers.
• Process unsubscribe requests promptly.

8. Links and Attachments That Use the Reputation of Other Domains

Filters also scan the domains in the body of your email, and these can negatively influence your deliverability.

Public link shorteners are a common source of problems because they are widely used by spammers. Tracking domains are another problem area. If your newsletter service uses a common tracking domain, you'll be linked to every other client who uses this domain.

Use a branded tracking domain, link to reputable websites, and keep the HTML simple. A large image with no text or an attachment from a new domain can be treated suspiciously by filters too. Always include a plain-text version.

Trigger words are less important today than many people think. Modern filters rely more on reputation and engagement than on the words in your messages. You can use "free" in your subject line if you are a trusted sender, but if your history is not perfect, you can have problems even if the message is squeaky clean.

9. Unexpected Volume Changes

Filters like regular volume. Sending 2,000 emails per week and then suddenly sending 80,000 emails at once looks like a compromised account.

If you are switching to a new IP or a new domain, or reactivating old mailing segments, increase volume gradually over several weeks, starting with your most engaged contacts. Keep a regular sending schedule and don't spam your list just because you have a promotion.

Why Your Emails Keep Landing in Spam

Spam placement usually comes from small gaps: a missing DKIM record, a third-party service not added to SPF, an old list that isn't regularly cleaned, or an IP address you know nothing about.

But the good news is that all of the points above can easily be checked and fixed. Start with authentication and alignment, because providers now require them. The next step is to check your infrastructure, your list hygiene, and how easy it is to unsubscribe from your email list. Check all of this every few months, because DNS records, third-party services, and providers' requirements can change.