Deliverability

Deliverability refers to the ability of an email to successfully reach the recipient's inbox without being blocked or marked as spam.

Early email systems had minimal filtering. Starting from the green card spam incident in the 90s, email providers began implementing spam filters to protect users from unwanted emails. Nowadays, email deliverability is a complex field involving various techniques and best practices to ensure that legitimate emails reach their intended recipients.

This guide will help you understand how to improve the deliverability of emails sent via Hyvor Relay.

Jump to each section:

• Content
• Technical Configurations
• Other Factors
• Blacklists
• Tools

Content

First rule for not getting marked as spam: do not send spam. With modern AI, it is even easier to detect spammy content.

• Send emails that are relevant to the recipients. Make sure they have opted in to receive your emails.
• Avoid spammy formatting, like using all caps, excessive exclamation marks, or overuse of certain words (like "free", "urgent", etc.).
• Include an unsubscribe link in all emails. This is also a legal requirement in many jurisdictions.
• Configuring a List-Unsubscribe header is highly recommended for all list-type emails.

Technical Configurations

Proper technical configurations are crucial for email deliverability. Here are some key configurations to consider:

• SPF Managed : DNS record that lists which IP addresses are allowed to send mail from the given MAIL FROM domain (not the From header)
• DKIM Managed : Cryptographically signs outgoing mail so receivers can verify authenticity. The domain in the DKIM signature should match the From header domain. Email providers verify the signature using a public key published in DNS.
• DMARC: DNS record that tells receivers how to handle emails that fail SPF or DKIM checks. It also provides reporting capabilities. The owner of the From domain should publish a DMARC record.
• Reverse DNS (PTR): Each sending IP address should have a PTR record that resolves back to a domain name. You should set up a PTR record for each sending IP address as explained in the Setup guide.
• FCrDNS Managed : The domain name used in the PTR record should resolve back to the same IP address.
• EHLO Managed : A properly formatted FQDN presented during SMTP handshake.
• TLS (STARTTLS) Managed : Ensures that emails are encrypted during transit between mail servers.
• Bounces & Suppressions Managed : Properly handling bounces and avoiding sending to suppressed addresses helps maintain a good sender reputation.
• Feedback Loops: Setting up feedback loops with major email providers allows you to handle spam complaints effectively. Hyvor Relay creates suppressions for addresses that mark your emails as spam (setup required)

Other Factors

There are other factors that affect email deliverability beyond content and technical configurations:

• Domain Age: Older domains generally have better deliverability than newly registered ones. This applies to both the instance domain and sending (FROM) domain. There is no quick fix for this; time is the only cure. Keep sending good emails consistently to those who expect them.
• Sender Reputation: Email providers maintain a reputation score for sending IP addresses and domains based on various factors like complaint rates, bounce rates, and spam trap hits. Suppressions, which Hyvor Relay handles, are important to avoid resending to addresses that have bounced or marked your emails as spam.
• Engagement Metrics: High open rates, click-through rates, and low complaint rates positively impact deliverability. Send high quality, relevant content to engaged recipients.
• Sending Volume & Frequency: Sudden spikes in sending volume can raise red flags. Maintain a consistent sending pattern. Hyvor Relay's API rate limits can help manage this.

Blacklists

Email providers depend on blacklists, usually maintained by a third party, to determine if an email is spam. They are primarily based on the sending IP address while some are based on the sending domain. Getting one of your IPs blacklisted can significantly affect all of your users' deliverability.

Most blacklists are public. Spamhaus, Barracuda, and SpamCop are some of the popular blacklists. They are usually DNS Blacklists (DNSBLs) and can be queried via DNS.

Some providers, such as Google, Yahoo, and Microsoft, maintain their own internal blacklists. They cannot be queried via DNS. The Email Providers page has more vendor-specific information.

Blacklists Health Check

Hyvor Relay has a health check to monitor the sending IPs for blacklisting on popular public blacklists. If any of the sending IPs are blacklisted there, an alert is shown in the Health section in sudo. See Health Check → Blacklists for more information.

Preventing Blacklisting

Here are some best practices to avoid getting blacklisted:

• Send emails only to users who have opted in to receive them.
• Use double opt-in to avoid spam traps. (Spam traps are email addresses that are not used by real users but are used to catch spammers.)
• Never use purchased email lists. They are often full of spam traps and inactive addresses.
• Make sure the unsubscribing process works correctly and is easy for the users.
• Set up Feedback Loops with major email providers to get notified when users mark your emails as spam.

Removing from Blacklists

If you find your sending IPs blacklisted, follow the removal procedures provided by each blacklist. This usually involves identifying and fixing the issues that led to the listing, then submitting a delisting request. In the Blacklists Health Check section, links to the removal procedures are provided for each blacklist.

Note that it is completely normal for a new sending IP or instance domain to be blacklisted initially. It may take some time and consistent good sending practices to build a positive reputation.

Tools

For testing email deliverability:

• Mail Tester: Send a test email to the provided address, and it will analyze various aspects of your email, including spam score, SPF, DKIM, DMARC, blacklists, and more.
• Mail Genius: Similar to Mail Tester, it provides a comprehensive analysis of your email's deliverability factors.
• Mailreach: Send emails to real inboxes across various email providers to see if they land in the inbox or spam folder.

For checking blacklists:

• MXToolbox Blacklist Check: Check if your sending IPs are listed on over 100 DNS-based blacklists.
• MultiRBL: Another tool to check your sending IPs against multiple DNS-based blacklists.