Email deliverability is a crucial factor in the success of your survey invitation campaigns. Whether you're sending invitations, reminders, or automated follow-ups, ensuring that your messages land in participants’ inboxes—not their spam folders—directly impacts your response rates.
This guide outlines the most important factors affecting deliverability, with actionable steps ordered by priority. These practices align with industry standards and new bulk email requirements from providers like Google and Yahoo.
1. Authenticate Your Email Domain
Modern spam filters rely on authentication to verify that your messages are legitimate. If your emails aren’t properly authenticated, they’re more likely to be rejected or filtered to spam.
You must configure all three authentication protocols:
- SPF (Sender Policy Framework)
- DKIM (DomainKeys Identified Mail)
- DMARC (Domain-based Message Authentication, Reporting & Conformance)
Use mail-tester.com to send a test email and verify your setup.
2. Maintain a Strong Sender Reputation
Mailbox providers (like Gmail, Outlook, and Yahoo) monitor your domain and IP reputation. A poor reputation leads to lower inbox placement and higher spam filtering.
Key factors affecting reputation:
- High bounce rates
- Spam complaints (keep below 0.3%)
- Sending behavior (volume spikes, inconsistent activity)
How to protect your reputation:
- Only email contacts who have opted in
- Remove invalid or bouncing addresses
- Avoid cold or purchased contact lists
3. Include a Clear Unsubscribe (Opt-Out) Link
To comply with regulations (GDPR, CAN-SPAM, CASL) and mailbox provider requirements, every bulk email must include an easy way for recipients to unsubscribe.
- Include a visible unsubscribe link in every message
- Use one-click unsubscribe headers. Email providers, such as Google and Yahoo, now require a one-click opt-out email header for bulk senders to ensure that recipients can quickly and easily unsubscribe.
This is also required under the Forsta Acceptable Usage Policy and helps reduce spam complaints, improving your domain’s reputation.
Further Reading:
4. Send Emails in Batches to Avoid Throttling
Sending a large number of emails in a short period can trigger throttling by email providers like Google, Yahoo, and Microsoft. Throttling means that the provider slows down or temporarily blocks incoming mail from your domain or IP.
To avoid this:
- Send in smaller batches instead of all at once
- Distribute your emails over time
- Slowly ramp up volume for new domains or IP addresses
You can use tools like:
- Google Postmaster Tools
- Microsoft SNDS
- Yahoo Complaint Feedback Loop
These tools help monitor your domain’s health and identify issues with delivery or spam complaints.
5. Write Clean, Professional Email Content
Spam filters still evaluate the content of your emails. Poor formatting or spam-like language can raise red flags.
Avoid:
- ALL CAPS or excessive punctuation (e.g. “ACT NOW!!!”)
- Spammy phrases: “Click here!”, “Once in a lifetime opportunity!”, “Guaranteed!”
- Starting subject lines with “Free”, “Hello”, “Buy”, or “$”
- Terms like “Life Insurance”, “Lose weight”, “Your family”
- Pharmaceutical names (e.g. Viagra, Cialis)
- Using large images with little or no text
- Unrelated links
Do:
- Use a natural, professional tone
- Include a balance of text and visuals
- Avoid image-only layouts
- Use a simple, clean HTML structure
- Include both HTML and plain text versions of your message
6. Keep Your Email List Clean and Engaged
A healthy list reduces bounces and spam complaints, and improves your chances of landing in the inbox.
Best practices:
- Remove hard bounces and inactive addresses regularly
- Avoid repeatedly emailing non-engaging recipients
- Use confirmed (double) opt-in when possible
- Don’t import outdated or purchased lists
7. Track Key Metrics to Monitor Performance
Even if your system doesn’t track open rates, you can still monitor several important metrics to assess deliverability:
- Delivery Rate – % of successfully delivered emails
- Bounce Rate – % of undelivered emails
- Hard Bounces: permanent issues (e.g., invalid address)
- Soft Bounces: temporary issues (e.g., mailbox full)
- Spam Complaint Rate – % of users marking your email as spam
- Unsubscribe Rate – % of recipients opting out
Watching these metrics helps you respond quickly to issues before they harm your sender reputation.
8. Test Before You Send
Before launching a large campaign, send test emails and review them for red flags.
- Use mail-tester.com to check authentication and spam score
- Check how your message displays across devices and inboxes
- Confirm that unsubscribe links and reply-to addresses are functioning correctly
Here are the bulk email sending guidelines from different mailbox providers and links to their support teams.
| Guidelines | Support Link | Postmaster Tools |
| Google - Guidelines | Google - Support Link | Google - Postmaster Tools |
| Yahoo - Guidelines | Yahoo - Support Link | Yahoo - Complaint Feedback Loop |
| Outlook - Guidelines |
You can setup Postmaster tools for your sender domain and monitor spam rate, overall health of the domain etc. You can also contact their support teams to lift any restrictions enforced on your sender domains.
Summary
Email deliverability isn’t just about avoiding spam filters - it’s about building a trustworthy sender reputation, respecting recipients, and sending thoughtful, relevant messages. Start with authentication, protect your domain’s reputation, and follow these best practices to maximize your email success.