DKIM (DomainKeys Identified Mail)
DKIM is an advanced email authentication technique that attaches a cryptographic signature to outgoing email headers, allowing the receiving server to confirm the email’s authenticity. The sending domain uses a private key to generate this signature, which is encrypted and linked to the email’s content. The recipient’s server then retrieves the public key from the domain’s DNS records to validate the signature. A valid DKIM signature confirms that the email is genuinely from the claimed sender and has not been altered during transmission, making it a powerful tool against email spoofing, phishing, and other types of email fraud.
SPF (Sender Policy Framework)
SPF is a protocol that helps email providers identify which servers are authorized to send emails on behalf of a particular domain. Domain owners create an SPF record in their DNS that lists authorized IP addresses and domains, helping prevent unauthorized entities from sending fraudulent emails using their domain name. When an email arrives, the receiving server checks the SPF record to verify if it originated from a valid source. If it didn’t, the email may be flagged as spam or rejected. SPF is a critical component in defending against domain spoofing and ensuring deliverability.
Spamhaus
Spamhaus is a non-profit organization that combats email spam by maintaining and providing real-time blocklists (RBLs) of known spam sources. These blocklists contain IP addresses, domains, and URLs associated with spam, phishing, malware, and botnet activities. Many email providers and businesses use Spamhaus’s RBLs to filter incoming emails, blocking messages originating from blacklisted sources. This service is highly valuable for maintaining email hygiene and securing inboxes from potentially harmful messages.
SURBL (Spam URI Realtime Blocklists)
Unlike IP-based blacklists, SURBL focuses on identifying suspicious or malicious URLs embedded within email messages. It contains databases of domains and URLs linked to spam and other malicious activities, including phishing and malware. When an email arrives, receiving servers can check URLs within the message body against the SURBL list. If a listed URL is detected, the email may be marked as spam or blocked. This method helps prevent spam by targeting the content within emails rather than just the sender.
Mailinblack
Mailinblack is a cybersecurity service that uses artificial intelligence and machine learning to filter incoming emails, distinguishing between legitimate and unwanted messages. It provides several layers of security, including sender authentication, challenge-response systems, and behavioral analysis, to protect against phishing, spam, and malware. Mailinblack also uses a user validation feature where unknown senders must verify themselves before their emails reach the recipient, thereby reducing the likelihood of unauthorized access and potential email-based attacks.
MXToolBox
MXToolBox is a popular suite of online diagnostic tools for analyzing email configurations and troubleshooting potential email issues. It offers checks for SPF, DKIM, DMARC records, blacklist status, MX record configuration, and SMTP diagnostics. Administrators can use MXToolBox to monitor domain health, spot DNS misconfigurations, and ensure that their email setup adheres to best practices for security and deliverability. This tool is particularly useful for identifying potential blockages that could harm email delivery rates.
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
DMARC builds on SPF and DKIM by enabling domain owners to specify policies for handling unauthenticated emails. Domain owners can set their DMARC record to instruct receiving servers on what to do with emails that fail SPF or DKIM checks (e.g., quarantine or reject). DMARC also provides reporting on failed authentication attempts, giving domain owners visibility into unauthorized use of their domain and helping them to detect potential spoofing attacks. DMARC compliance can improve deliverability and increase trust among recipients.
IP Warming
IP warming is the gradual process of ramping up the email volume sent from a new IP address to establish a reputation with ISPs. This is especially crucial for companies switching to a new IP or initiating high-volume campaigns, as sending a large volume of emails from an unknown IP can trigger spam filters. By gradually increasing the volume, ISPs see consistent, trustworthy sending patterns, which reduces the likelihood of messages being marked as spam. Successful IP warming leads to better inbox placement and improved sender reputation.
Bounce Rate
Bounce rate represents the percentage of emails that were undeliverable and returned to the sender. Bounces are categorized into two types: soft bounces (temporary issues, like a full inbox or server down) and hard bounces (permanent issues, like an invalid email address). High bounce rates can damage sender reputation and lead to deliverability issues. Regularly cleaning email lists to remove inactive or invalid addresses is a common practice to keep bounce rates low.
Open Rate
Open rate is the percentage of email recipients who open a specific email. This metric provides insights into the effectiveness of subject lines, sender reputation, and audience interest in the brand. Open rates are calculated by dividing the number of unique email opens by the total number of emails delivered. While open rate is valuable for tracking engagement, it should be analyzed alongside other metrics like CTR for a fuller picture of email campaign success.
CTR (Click-Through Rate)
CTR measures the percentage of email recipients who clicked on one or more links within an email. It’s a key performance indicator for engagement and content relevance, often calculated by dividing the number of clicks by the number of delivered emails. Higher CTRs indicate that email content resonates with recipients, while low CTRs can signal the need for adjustments in email copy, design, or targeting.
ESP (Email Service Provider)
An ESP is a platform or service for managing and distributing email campaigns. Major ESPs like Mailchimp, SendGrid, and Campaign Monitor offer features such as list segmentation, automation, analytics, and campaign scheduling. ESPs also provide templates and tools for designing emails and tracking metrics, making it easier to reach and engage large audiences effectively.
Sender Score
Sender Score is a reputation score assigned to a sender’s IP address, reflecting factors like complaint rates, bounce rates, and engagement rates. Scores range from 0 to 100, with higher scores indicating greater trustworthiness. ISPs consider sender scores when determining whether to filter, block, or deliver emails. Regularly monitoring sender score and following best practices can help maintain high deliverability.
Suppression List
A suppression list is a database of email addresses that should not receive future emails, typically including unsubscribers, spam reporters, and hard bounces. Using a suppression list helps prevent unnecessary complaints, maintains compliance with regulations like CAN-SPAM, and ensures emails only reach those who want them, improving list quality and sender reputation.
Whitelist
A whitelist is a list of approved IP addresses or domains recognized as trustworthy by an email provider or filter. Emails from whitelisted senders are often exempt from certain spam checks, ensuring they reach the inbox. Companies often whitelist trusted partners to ensure that critical messages aren’t blocked by spam filters.
Blacklist
A blacklist is a list of IP addresses or domains known to send spam or malicious content. Blacklisted IPs or domains face severe deliverability issues, as emails from these sources are often automatically filtered or blocked by email providers. To avoid blacklisting, it’s essential to maintain a clean email list, avoid sending spammy content, and monitor sender reputation.
Spam Score
Spam score is a predictive metric estimating the likelihood of an email being marked as spam. Various tools, like SpamAssassin, assign scores based on factors like keywords, sender reputation, and formatting issues. Minimizing spammy characteristics in email content and adhering to best practices can help keep spam scores low and improve inbox placement.
Seed List
A seed list is a small set of email addresses used for testing and monitoring deliverability across different ISPs and devices. Marketers use seed lists to check whether emails reach recipients’ inboxes and appear correctly. Seed lists provide insights into the deliverability and effectiveness of email campaigns, helping marketers address issues proactively.
Double Opt-In
Double opt-in is a subscription process where new subscribers must confirm their interest in receiving emails by clicking a link in a confirmation email. This extra step ensures that recipients genuinely want to receive emails, reducing spam complaints and maintaining list quality.
List Hygiene
List hygiene is the process of regularly cleaning and maintaining an email list to remove inactive or invalid addresses. Good list hygiene reduces bounce rates, maintains sender reputation, and improves deliverability. Common list hygiene practices include removing hard bounces, inactive subscribers, and duplicates.
CAN-SPAM Act
The CAN-SPAM Act is a U.S. law that establishes rules for commercial email, including the requirement for an unsubscribe link, accurate sender information, and truthful subject lines. Violating CAN-SPAM can lead to legal penalties, so adhering to these guidelines is essential for compliance and building trust with subscribers.
A/B Testing
A/B testing, or split testing, involves sending two variations of an email to different segments of an audience to see which one performs better. A/B testing can focus on subject lines, visuals, CTA buttons, or content. Results provide valuable insights for optimizing email campaigns and improving engagement.
Email Throttling
Email throttling is the practice of controlling the rate of email delivery to avoid overloading ISPs and triggering spam filters. Throttling emails by gradually sending them improves deliverability and reduces the risk of emails being marked as spam, especially in high-volume campaigns.
Greylisting
Greylisting is a spam-filtering technique where the receiving server temporarily rejects an email on its first attempt. Genuine servers retry, while many spam bots do not, so the email is eventually accepted. Greylisting helps reduce the volume of spam reaching recipients by filtering out less persistent senders.
Dynamic Content
Dynamic content is email content that changes based on recipient data, such as location, preferences, or behavior. By tailoring content to individual recipients, dynamic content boosts relevance, engagement, and personalization, leading to higher open and click-through rates.
