Cold email senders obsess over subject lines, personalization, targeting, and timing; but one of the fastest ways to get flagged by spam email filters in 2025 is also one of the most overlooked:

Including links in your cold emails.

Most senders assume links are harmless. But to modern spam filters, links represent uncertainty, redirection risk, and possible phishing; all major signals inside today’s AI-driven spam filtering systems.

And because spam email filtering is stricter than ever across Gmail, Outlook, and Office 365, even legitimate emails with perfect authentication can end up filtered as spam simply because of the URLs inside the message.

So if you’re running outbound campaigns or sending high-volume B2B email, here’s the new deliverability rule:

Avoid links in cold emails entirely.

Below is the breakdown of why spam filtering services flag links so aggressively, how Gmail and Office 365 interpret URLs, and what serious senders must do to protect cold email deliverability in 2025.

How Spam Filters Evaluate Links (and Why They Penalize Them)

Modern spam filtering software doesn’t just scan for suspicious words. It analyzes the entire email infrastructure behind your message, including every URL.

This is how filtering spam works in practice:

1. URL reputation checks

Any time you include a link, Gmail and Outlook run the URL through their spam filtering service reputation database.
If the destination domain has low trust or appears on blocklists, your entire message is penalized, even if your sending domain is healthy.

This applies to enterprise systems too, like Barracuda spam filtering, which many corporate networks use.

2. Redirect chains look like phishing

Shorteners like Bitly and smartlinks add multiple redirect hops that gmail spam filters and office 365 filtered as spam systems treat as phishing patterns.

3. Link-to-text ratio

Human emails rarely contain multiple links.
Emails with several URLs resemble promotional blasts and are flagged by the best spam filters.

4. Mismatched URLs

If the text says one thing but the hyperlink goes elsewhere, that’s a major red flag in spam email filtering.

5. Words that trigger spam filters

Filters score both links and the language around them.
Phrases associated with sales pressure or urgency raise filtering scores, especially when combined with URLs.

Why DMARC Matters: How to Stop Your Emails From Landing in Spam

2025 Trend: Link-Free Cold Emails Perform Better

Deliverability data from agencies and SaaS teams shows the same pattern:

Cold emails with no links at all outperform linked emails in inbox placement, replies, and domain reputation.

Why?

Because link-free messages appear:

• Human
• Non-automated
• Low-risk
• Conversation-driven

This aligns with 2025 sending best practices and what spam filtering services now expect from legitimate 1:1 outreach.

How Warm Up Really Works (and Why It Matters for Deliverability)

What to Use Instead of Links

Modern cold email relies on soft CTAs that inspire replies instead of clicks.
Replies generate positive engagement signals, which improve your cold email deliverability and domain reputation.

Examples:

• “Want me to send the details?”
• “Should I send over an example?”
• “Want the short breakdown?”
• “Open to seeing a quick case study?”

These link-free CTAs outperform “Click here” or “Schedule a call”, and they protect your sending domain.

Removing Links Isn’t Enough — You Still Need Infrastructure

Even without links, your emails must pass authentication and reputation checks.

To consistently avoid spam email filtering, you need:

• SPF, DKIM, and DMARC alignment
• Proper domain warm-up
• Dedicated SMTP relay (never shared)
• Real-time deliverability testing
• Blacklist monitoring
• Domain-aged sending
• Spam placement insights

Mission Inbox handles all of this behind the scenes, giving your emails the best possible chance of bypassing Gmail, Outlook, and Barracuda spam filtering systems.

SMTP Infrastructure Explained: Shared vs Dedicated IP

If You Absolutely Must Send Links (Transactional Only)

For transactional emails — not cold outreach — links may be required.

Follow these rules:

• Use a verified subdomain for tracking
• Never use shorteners
• Avoid more than one link
• Keep the URL text identical to the destination
• Run an email deliverability test before sending

Your safest option is Mission Inbox’s deliverability testing tool, which flags risky URLs and identifies domains likely to be blocked by spam email filters.

How to Improve Email Deliverability in 2025

Final Takeaway: Spam Filters Don’t Hate Links; They Hate Risk

Your cold email doesn’t get filtered because Gmail dislikes marketing.
It gets filtered because links are one of the strongest phishing indicators in any spam filtering service.

In 2025, the safest outbound strategy is simple:

No links.
Plain text.
Conversation-first.
Supported by professional email infrastructure.

If you want to know exactly how spam filters see your messages — and how to avoid getting flagged — run a deliverability test with Mission Inbox.

Run your deliverability test at MissionInbox.com