How email deliverability works

This guide covers how email deliverability works, what factors determine whether your emails reach the inbox, and what actions you can take in Sender to improve your results.

Why this matters

Email deliverability is the ability of your emails to reach the recipient's inbox rather than being filtered to spam or blocked entirely. Mailbox providers such as Gmail, Yahoo, and Outlook evaluate every incoming email based on the sender's reputation, authentication setup, content quality, and subscriber engagement. Poor deliverability means your campaigns go unseen, regardless of how many emails you send. Understanding the factors that affect deliverability helps you take the right actions to protect your sender reputation and maintain consistent inbox placement.

Recommended practices

Authenticate your sending domain

Domain authentication tells mailbox providers that you are a legitimate sender and that your emails have not been tampered with. Set up SPF, DKIM, and DMARC records for your sending domain. In Sender, go to Account settings → Domains to check whether your domain's Ownership confirmed and Authentication columns show verified status. Unauthenticated emails are far more likely to be filtered to spam or rejected outright.

Warm up new sending domains gradually

When you start sending from a new domain or return after a long period of inactivity, mailbox providers have no history to evaluate your reputation. Sending a large volume immediately can trigger spam filters. Start with a small batch of emails to your most engaged subscribers — those who have recently opened or clicked — and increase volume steadily over 2–4 weeks. Monitor your Bounce rate and Average spam rate on the Dashboard during this period to catch problems early.

Send to engaged subscribers

Engagement — opens, clicks, and replies — is one of the strongest signals mailbox providers use to determine inbox placement. Subscribers who do not interact with your emails signal to providers that your content may be unwanted. Create segments in Subscribers → Segments that target contacts who have opened or clicked within the last 30–90 days. Prioritize these segments for your campaigns. This directly improves the engagement signals mailbox providers track.

Maintain list hygiene

Invalid and inactive addresses on your list increase your bounce rate and reduce engagement, both of which damage your sender reputation. Regularly review subscribers with a Bounced status by filtering with the Email status dropdown on the Subscribers page. Remove or suppress contacts who have not engaged in 90–180 days. Never use purchased or scraped email lists — these contacts have not opted in and will generate bounces and spam complaints.

Keep sending volume and frequency consistent

Sudden spikes in email volume are a red flag for mailbox providers. If you typically send 5,000 emails per week and suddenly send 50,000, providers may throttle or block your messages. Establish a regular sending schedule and stick to it. Use the Traffic and reach report on the Dashboard to track your Total emails sent over time and verify your sending patterns remain stable.

Key metrics to watch

Bounce rate — The percentage of sent emails that were not accepted by the recipient's mail server. Found on the Dashboard under the Traffic and reach report section. A bounce rate above 2% indicates list quality issues that need attention.

Hard bounce rate — The percentage of emails that permanently failed, typically due to invalid or non-existent addresses. Displayed on the Dashboard below the main chart. Any hard bounce rate above 0.5% suggests your list contains outdated or incorrect addresses that should be removed.

Average spam rate — The percentage of recipients who marked your email as spam. Shown on the Dashboard alongside bounce metrics. Keep this below 0.1% — exceeding this threshold can cause providers like Gmail to route your emails to spam.

Unsubscribe rate — The percentage of recipients who unsubscribed after receiving your email. Visible on the Dashboard and in each campaign's Statistics section under the Campaign overview. A rising unsubscribe rate may indicate your content is not matching subscriber expectations or you are sending too frequently.

Opened and unique clicks — Engagement metrics that indicate whether recipients are interacting with your content. Found in the Statistics section of each campaign's Campaign overview page. Consistently low open or click rates suggest your subject lines, content, or sending times need adjustment, and may negatively affect inbox placement over time.

Common mistakes

Sending to your entire list without segmentation → Mailbox providers weigh engagement heavily. Sending to unengaged subscribers drags down your open and click rates, which signals low-quality sending. Use Subscribers → Segments to target active subscribers.

Ignoring bounces → Continuing to send to addresses that bounce damages your sender reputation. Filter by Email status → Bounced on the Subscribers page to identify and remove invalid addresses after every campaign.

Using a purchased or rented email list → These contacts have not opted in to your emails. Sending to them generates high bounce rates, spam complaints, and can lead to account suspension. Build your list through organic opt-in methods only.

Sending inconsistently → Long gaps between sends followed by large blasts make your sending pattern unpredictable to mailbox providers. Maintain a regular schedule and use the Dashboard to monitor volume trends.

Skipping domain authentication → Without SPF, DKIM, and DMARC, mailbox providers cannot verify your identity. This significantly increases the chance of your emails being filtered to spam. Verify your authentication status under Account settings → Domains.

FAQs

What is the difference between delivery rate and inbox placement?

Delivery rate measures the percentage of emails accepted by the recipient's mail server — it does not mean they reached the inbox. Inbox placement measures how many of those accepted emails actually land in the inbox versus the spam folder. You can have a high delivery rate while many emails still go to spam.

How long does it take to warm up a new sending domain?

A typical warm-up takes 2–4 weeks. Start by sending small volumes to your most engaged subscribers and gradually increase the amount each day or week until you reach your full sending capacity. Monitor your Bounce rate and Average spam rate on the Dashboard throughout the process.

Does Sender automatically handle hard bounces?

Sender manages hard bounces according to its bounce handling policies. You can check a subscriber's status by using the Email status filter on the Subscribers page. Contacts marked as Bounced will not receive further emails. You can also manually review and clean bounced contacts from your list.

How do spam complaints affect my deliverability?

Mailbox providers track your spam complaint rate closely. If your Average spam rate exceeds approximately 0.1%, providers like Gmail may begin routing your emails to spam. Monitor Total spams and Average spam rate on the Dashboard and investigate any spikes immediately.

Should I buy an email list to grow my audience?

No. Purchased lists contain addresses that have not opted in to receive your emails. This leads to high bounce rates, spam complaints, and potential account suspension. Build your list organically using signup forms and lead magnets so every subscriber has chosen to hear from you.

Why are my emails going to spam even though my delivery rate is high?

A high delivery rate only means the mail server accepted your emails — it does not control inbox placement. Common causes of spam folder placement include missing domain authentication, low engagement rates, high spam complaint rates, or content that triggers spam filters. Review your Average spam rate and engagement metrics on the Dashboard and verify your domain authentication under Account settings → Domains.