Why is email authentication so crucial for deliverability?

Email authentication, primarily SPF, DKIM, and DMARC, helps verify that your emails are legitimate and prevents spoofing. Without proper authentication, mailbox providers may flag your emails as suspicious, leading to them being sent to spam or rejected. It validates that you are authorized to send emails from your domain.

What's wrong with buying email lists?

Purchased email lists often contain invalid addresses, spam traps, and unengaged contacts. Sending to such lists results in high bounce rates and spam complaints, which severely damage your sender reputation and can lead to your domain or IP being blacklisted (or blocklisted) by mailbox providers.

How do low engagement rates affect email deliverability?

Low engagement rates (e.g., low opens, low clicks) signal to mailbox providers that your content is not relevant or desired by recipients. This negative feedback can decrease your sender reputation over time, causing future emails to be delivered less reliably. High unsubscribe rates and spam complaints also fall into this category.

What is IP/domain warm-up and why is it important?

Warm-up involves gradually increasing your email sending volume over time from a new IP or domain. This allows mailbox providers to recognize your sending patterns as legitimate and build a positive reputation. Skipping warm-up can cause sudden high volumes to be seen as suspicious, leading to throttling, rejections, or blacklisting (blocklisting).

What are some poor sending practices to avoid that can cause issues with email deliverability? - Sender reputation - Email deliverability - Knowledge base

Email deliverability is about ensuring your emails reach the intended inbox, not the spam folder or nowhere at all. It's a complex dance involving technical configurations, sender reputation, content quality, and recipient engagement. Even small missteps can lead to significant issues, impacting your communication efforts and ultimately, your bottom line.

Many factors contribute to poor deliverability, but they often stem from poor sending practices. Understanding these pitfalls is the first step toward improving your email program and building a reliable connection with your audience. I'll highlight some of the most common mistakes I see senders make and how to avoid them.

Poor sender reputation and list hygiene

Your sender reputation is arguably the single most important factor in email deliverability. It's like a credit score for your email sending, built over time based on how recipients interact with your emails and your adherence to best practices. A poor reputation can lead to emails being blocked, throttled, or sent straight to the spam folder. Building a strong sender reputation and maintaining it requires consistent effort and careful attention to your sending habits.

One of the quickest ways to damage your sender reputation is by sending to a poorly managed or acquired email list. This includes purchasing email lists, which are almost always fraught with deliverability risks like spam traps and invalid addresses. Sending to unengaged or old contacts also signals to mailbox providers that you're not managing your list effectively, leading to lower engagement rates and higher complaint rates, both of which negatively impact your reputation. Regularly cleaning your list is key to ensuring your emails reach active, interested recipients.

How your email sending practices impact your domain reputation is critical. When your sender reputation takes a hit, it becomes incredibly difficult to recover. Mailbox providers like

Gmail and

Outlook are increasingly strict, requiring domains to have a solid history of good sending behavior.

The danger of bad lists

Purchased lists: These lists often contain a high percentage of invalid email addresses and spam traps. Sending to them can immediately flag your domain as a spammer and lead to blacklisting (or blocklisting). Purchased email lists cause deliverability issues because they often contain spam traps, leading to significant reputation damage.
Inactive subscribers: Continuing to send emails to recipients who haven't engaged in a long time increases the likelihood of complaints and low engagement, which hurts your sender reputation. It's often better to remove or re-engage these contacts.
Spam traps: These are email addresses designed to catch spammers. Hitting one indicates poor list acquisition or hygiene, leading to immediate blacklisting (or blocklisting) and severe reputation damage. Learn about different types of spam traps and how they work.

Technical configuration and authentication failures

Email authentication is a critical technical foundation for deliverability. SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) are protocols that verify your emails are legitimate and prevent spoofing. Failing to implement these or having incorrect configurations can lead to your emails being flagged as suspicious or outright rejected by recipient servers.

A common mistake is sending marketing or transactional emails from a free email domain like

AOL.com,

Yahoo.com, or

Gmail.com. These domains are easily spoofed by spammers, and most professional senders use their own custom domains. Mailbox providers expect legitimate businesses to send from their own authenticated domains. Failing to use best practices for email sender addresses will hinder your deliverability.

It's not enough to just have these records, they must be configured correctly. Issues like SPF lookup limits, DKIM signature errors, or a DMARC policy that is too lenient (or missing altogether) can severely impact your ability to reach the inbox. We have a simple guide to DMARC, SPF, and DKIM to help you get started.

Example DMARC record to start with

v=DMARC1; p=none; rua=mailto:reports@yourdomain.com; ruf=mailto:forensics@yourdomain.com; fo=1;

Poor content and engagement strategies

The content of your emails also plays a significant role in deliverability. Spam filters are constantly evolving, and certain elements within your email can trigger them, leading to your messages being diverted to the junk folder. This includes the subject line, body text, image-to-text ratio, and even the use of certain fonts or colors.

Spammy subject lines are a classic deliverability pitfall. Overuse of all caps, excessive exclamation marks, buzzwords (like "free," "guarantee," "win"), or deceptive phrasing can immediately raise red flags. Similarly, if your email content is too image-heavy with minimal text, it can be seen as suspicious, as spammers often use images to bypass text-based filters. A balanced email template can trigger spam filters if it's not well-designed.

Beyond explicit spam triggers, low engagement rates are a strong signal of poor content. If recipients consistently don't open your emails, delete them without reading, or mark them as spam, it tells mailbox providers that your content isn't valuable. This, in turn, hurts your sender reputation and subsequent deliverability. This feedback loop is crucial to understand.

Finally, making it difficult for recipients to unsubscribe is a critical error. Not only is it often illegal (e.g., CAN-SPAM Act compliance), but it also frustrates users, leading them to mark your email as spam instead of finding an unsubscribe link. A clearly visible and easy-to-use unsubscribe option is essential for maintaining a healthy list and avoiding spam complaints. Mailbox providers are increasingly prioritizing user experience, so a clear unsubscribe path is paramount for good standing.

Aspect	Poor Practice (Spam Risk)	Best Practice (Deliverability Boost)
Subject lines	Using all caps, excessive exclamation marks, and generic spam phrases like "FREE MONEY NOW!!!"	Clear, concise, and relevant to the email's content. Use personalization where appropriate.
Image-to-text ratio	Sending emails that are primarily one large image with little to no text. Mailbox providers see this as a red flag.	Maintain a balanced image and text ratio. Use descriptive alt text for images.
Engagement	Ignoring low open rates, high bounce rates, and increasing spam complaints.	Monitor engagement metrics closely. Segment your list to send relevant content and actively re-engage or remove inactive subscribers. Regularly check Google's sender guidelines.
Unsubscribe process	Hiding the unsubscribe link or making the process overly complicated (e.g., requiring multiple steps or a login).	Provide a clear, one-click unsubscribe option that is easy to find in every email. This reduces spam complaints.

Ignoring sending volume and frequency

The volume and frequency of your email sends can also significantly impact deliverability. Sending too many emails too quickly, especially from a new or previously inactive IP address or domain, can trigger spam filters and lead to throttling or blocks. This is often seen as suspicious behavior, akin to a sudden surge of unsolicited mail.

Conversely, sending too infrequently can also be detrimental. If you have a large list but only email them sporadically (e.g., once every six months), recipients may forget they opted in, leading to higher spam complaints and unsubscribes. Establishing a consistent, moderate sending cadence is important. For new sending IPs or domains, a gradual email warm-up process is essential to build trust with mailbox providers and avoid issues like greylisting.

Warming up your IP/domain

When you start sending from a new IP address or domain, or after a long period of inactivity, you should begin with small volumes and gradually increase them. This process, known as warming up, builds a positive sending history and reputation with mailbox providers. Rushing this process by sending a large blast initially can trigger filters and land your emails on a blacklist (or blocklist). Mailbox providers monitor sending behavior, and sudden spikes in volume from unestablished senders are seen as highly suspicious. According to Spamhaus Technology, poor sending practices can trigger informational listings, highlighting the dangers of not managing bounces correctly as well.

Views from the trenches

Best practices

Always use a double opt-in process for new subscribers to ensure explicit consent and reduce the risk of spam complaints.

Regularly clean your email lists by removing inactive subscribers, hard bounces, and known spam traps to maintain high list quality.

Implement and correctly configure SPF, DKIM, and DMARC records to authenticate your emails and protect your sending domain.

Craft clear, concise, and valuable email content with a balanced image-to-text ratio to engage recipients and avoid spam filters.

Provide an easy-to-find, one-click unsubscribe option in all your emails to reduce spam complaints and improve user experience.

Common pitfalls

Sending emails from unauthenticated free email domains, which significantly harms sender reputation and deliverability.

Ignoring low engagement rates (opens, clicks) or high bounce and complaint rates, which signals to ISPs that your emails are not valued.

Making the unsubscribe process difficult or hidden, leading frustrated recipients to mark your emails as spam.

Sending large email volumes from a new or cold IP/domain without a proper warm-up plan, triggering spam filters and blocks.

Using deceptive subject lines or excessive spam trigger words, which immediately flags emails for junk folders.

Expert tips

Monitor your domain and IP reputation using tools like Google Postmaster Tools to identify issues early and proactively.

Segment your audience and personalize content to improve engagement, as tailored emails are more likely to be opened and clicked.

Prioritize recipient engagement metrics (opens, clicks, replies) over raw send volume to cultivate a positive sending reputation.

Regularly test your email deliverability to various mailbox providers to identify and troubleshoot potential issues before they escalate.

Stay updated on sender requirements from major mailbox providers, such as Gmail and Yahoo, as guidelines evolve frequently.

Marketer view

Marketer from Email Geeks says that understanding how different email service providers (ESPs) categorize and manage internal suppression lists (or blocklists) can be challenging due to a lack of transparency.

August 16, 2022 - Email Geeks

Marketer view

Marketer from Email Geeks says that frustratingly, some internal lists maintained by ESPs feel like mystical blocklists that don't serve the sender, suggesting direct action like unsubscribing or deleting contacts from databases might be more effective.

August 16, 2022 - Email Geeks

Building a stronger email program

Avoiding poor sending practices is not just about staying out of the spam folder, it's about building a trusted communication channel with your audience. By focusing on list hygiene, proper technical setup, engaging content, and responsible sending volumes, you can significantly improve your email deliverability and ensure your messages consistently reach the inbox.

Remember, email deliverability is an ongoing effort that requires continuous monitoring and adaptation. Staying informed about industry changes and regularly reviewing your practices will help you maintain a strong sender reputation and achieve consistent inbox placement. You can also review our guide on best practices for email deliverability and avoiding spam filters.