Why Emails Land in Spam

Email providers like Gmail and Outlook use hundreds of signals to decide whether your email reaches the inbox or gets buried in spam. The good news: most of these signals are within your control. This guide covers the most impactful deliverability practices you should follow.

1. Sending Volume - Steady and Gradual Wins

The number one mistake in cold email is sending too much, too fast. Email providers flag sudden spikes in volume as suspicious behavior.

Guidelines

New accounts: Start with 10 campaign emails per day per account after warmup is complete.
Ramp gradually: Increase by 5–10 emails/week each week if your metrics stay healthy.
Safe ceiling: Most practitioners cap at 20 campaign emails per day per inbox. Beyond that, use additional inboxes.
Use Prospi's daily sending limits to enforce caps per campaign and per account so you never accidentally over-send.

2. Email Content - Write Like a Human

Spam filters analyze your email content for patterns commonly associated with spam. Here is how to write emails that pass.

Do

Write short, conversational emails (50–120 words is ideal)
Use plain text - avoid HTML, images, and fancy formatting
Personalize the first line with something specific to the recipient
Include a clear, low-friction call to action
Use your real name and a professional signature
Use spintax

Do Not

Use spam trigger words excessively: "free," "guarantee," "act now," "limited time," "click here"
Include more than one link (your calendar link is usually sufficient)
Attach files in cold emails - ever
Use ALL CAPS or excessive exclamation marks!!!
Include an unsubscribe link in the first email (this signals bulk sending - handle opt-outs manually or via Prospi's built-in system)
Use URL shorteners (bit.ly, etc.) - they are heavily flagged by spam filters
Copy-paste the same template to everyone - even small variations help

3. Domain Age & Reputation

A brand new domain has zero reputation. Email providers treat unknown senders with suspicion.

Best Practices

Buy domains early - Purchase your sending domains 2–4 weeks before you need them. Let them age.
Use Prospi for domain purchases - Domains purchased through Prospi start with a clean reputation and are optimized for cold outreach.
Separate your sending domains - Never send cold email from your primary business domain. Use alternate domains (e.g., getprospi.com, tryprospi.com) to protect your main domain's reputation.
Set up a basic website - Even a simple landing page on your sending domain adds legitimacy.
Configure DNS authentication - SPF, DKIM, and DMARC must be set up correctly. See our SPF, DKIM & DMARC Setup Guide.

4. List Hygiene - Clean Data, Clean Reputation

Sending to bad email addresses is one of the fastest ways to affect your sender reputation. High bounce rates signal to providers that you are sending unsolicited email to purchased or scraped lists.

How Prospi Keeps Your Lists Clean

Built-in email verification - Prospi verifies every email address using Prospi's verification system plus catchall detection before sending.
Double-verified lead database - If you source leads from Prospi's database, they are already double-verified.
Auto-pause on high bounce rates - Prospi automatically pauses campaigns if bounce rates exceed safe thresholds, protecting your reputation.

Additional List Hygiene Tips

Remove hard bounces immediately (Prospi does this automatically)
Clean imported lists before uploading - do not trust external data without verification
Remove recipients who have not engaged after 3+ touchpoints
Watch for role-based addresses (info@, support@, admin@) - these often have lower engagement

5. Sending Infrastructure

Your technical setup directly impacts deliverability.

Use 2–3 email accounts per domain - This distributes volume and reduces the risk of any single account getting flagged.
Keep warmup running - Even while campaigns are active, warmup generates positive engagement signals.
Rotate sending accounts - Prospi can distribute campaign sends across multiple accounts automatically.
Monitor blacklists - Check your sending IPs and domains against blacklists regularly using tools like Prospi.

6. Engagement Signals

Email providers track how recipients interact with your emails. Positive signals improve your future inbox placement.

Replies are gold - A replied-to email tells providers your message was wanted. Optimize your emails for replies.
Opens matter less than they used to - Apple Mail Privacy Protection inflates open rates. Focus on reply rates instead.
Spam reports are critical - Even a small number of recipients marking you as spam can tank your reputation. Write relevant, targeted emails to minimize this.