Should I configure SSL or TLS on my sending domains for email marketing?
Matthew Whittaker
Co-founder & CTO, Suped
Published 20 Apr 2025
Updated 16 Aug 2025
6 min read
When delving into email deliverability, a common question arises regarding the necessity of configuring SSL or TLS on sending domains, especially for email marketing. It can be a bit confusing given how these technologies are often discussed in the context of websites. Understanding the distinctions and applications for email is crucial for maintaining strong sender reputation and ensuring your messages reach the inbox.
While SSL (Secure Sockets Layer) was once the standard for secure communication, it has largely been superseded by TLS (Transport Layer Security). For email, the focus is almost entirely on TLS due to its improved security features and patch of vulnerabilities found in older SSL versions. This transition is important to note because, while people still often use "SSL" generically, the underlying technology for current email encryption is TLS.
The role of TLS in email transmission
For email, particularly for bulk sending and marketing, TLS is the accepted standard for encrypting mail in transit. This is often implemented via STARTTLS, which upgrades an insecure connection to an encrypted one over standard SMTP ports. It ensures that the content of your emails, from sender to receiver, remains private and protected from eavesdropping.
Major mailbox providers, including Google and Yahoo, strongly encourage, and in some cases, require the use of TLS for email transmission. This is part of their broader efforts to secure the email ecosystem and combat spam and phishing. Sending emails over unencrypted connections can flag your mail as suspicious, even if it doesn't lead to immediate rejection.
While directly affecting inbox placement is not always a given for MTA-to-MTA TLS, it is a foundational security measure. It contributes to your overall sender reputation by demonstrating adherence to modern security practices. Some email clients, like Gmail, even display a lock icon or a warning if an email was not sent over an encrypted session, alerting recipients to potential privacy concerns. This can subtly impact how your subscribers perceive your brand.
Ensuring TLS is active
You can check if a receiving mail server supports TLS by performing a simple command line query, which shows the encryption capabilities. Look for the STARTTLS keyword in the server's response.
Check for STARTTLS supportBASH
telnet mail.example.com 25
EHLO yourdomain.com
SSL for tracking and image domains
Beyond the actual email transmission, the security of links and images embedded within your email campaigns is also vital. If your email marketing includes tracked links or hosted images that use your sending domain, these should absolutely be served over HTTPS, which relies on SSL/TLS certificates.
Having HTTPS (secure connections) for your tracking domains and image hosting ensures that your subscribers' interactions with your emails (like clicking links) are also secure. This is where an SSL certificate on these subdomains becomes directly relevant. Browsers and email clients will warn users about insecure HTTP links, potentially deterring clicks and impacting engagement, and by extension, your sender reputation. It's not just about the email itself, but the entire user experience your email provides.
Moreover, some providers may consider the presence of an SSL certificate on your tracking domains as a signal of a legitimate and professionally managed sending operation. This can contribute positively to your domain's overall standing and its ability to land in the inbox.
Non-secure link experience
Browser warnings: Users may see security warnings when clicking http:// links.
Reduced trust: Perceived as less professional or even suspicious by recipients.
Deliverability risk: Can negatively impact sender reputation with some mailbox providers.
Secure link experience
Smooth navigation: Seamless experience for users, no warnings.
Enhanced trust: Builds confidence and professionalism.
Improved deliverability: Aligns with modern sender best practices, benefiting inbox placement.
Deliverability and sender reputation considerations
While securing your email transmission and tracking links with TLS/SSL is a strong best practice, it's not the sole determinant of email deliverability. Mailbox providers assess a wide range of factors when deciding whether to deliver your email to the inbox, spam folder, or reject it entirely. These factors include but are not limited to, email authentication (SPF, DKIM, DMARC), sender reputation, content quality, and recipient engagement.
Failing to implement TLS for your email transmission might not result in immediate blocklisting (or blacklisting), but it can contribute to a poorer overall sender score over time. It signals a lack of commitment to security, which can indirectly affect how your emails are treated, especially by sophisticated filters used by companies like Google and Microsoft. Maintaining a robust domain reputation requires a holistic approach to email security and best practices.
For tracking domains or subdomains, the impact of not having an SSL certificate can be more direct. If your tracking links start with http:// instead of https://, it can create a jarring experience for recipients, particularly as web browsers increasingly flag non-HTTPS sites as insecure. This can lead to lower click-through rates and, ultimately, a diminished return on your email marketing efforts.
Authentication: Ensure your sending domains have properly configured SPF, DKIM, and DMARC records.
List hygiene: Regularly clean your email lists to remove inactive or invalid addresses.
Engagement: Encourage positive engagement (opens, clicks, replies) and minimize complaints and unsubscribes.
By addressing these broader aspects in conjunction with TLS for email transmission and SSL for tracked links, you build a comprehensive strategy that significantly boosts your deliverability and strengthens your sender reputation.
Final recommendation
While SSL and TLS are often used interchangeably, it is important to remember that TLS is the modern, secure protocol for email encryption. Configuring TLS on your sending domains for SMTP transmission, particularly STARTTLS, is a non-negotiable best practice for modern email marketing. It ensures that your emails are encrypted in transit, protecting sensitive data and aligning with the security expectations of major mailbox providers.
Equally important is applying SSL certificates to any subdomains you use for click tracking or hosting images within your emails. This enhances user trust, prevents browser warnings, and contributes to a professional brand image. While TLS alone might not directly guarantee inbox placement, it's a critical component of a robust email deliverability strategy that, when combined with strong authentication and good sending practices, will significantly improve your email marketing performance.
Views from the trenches
Best practices
Always prioritize enabling TLS 1.2 or higher for all outbound email connections to ensure modern encryption standards are met.
Obtain and apply SSL certificates for any subdomains used for link tracking, image hosting, or landing pages within your emails.
Regularly monitor your email logs and deliverability reports to ensure a high percentage of your emails are delivered over TLS encrypted sessions.
Common pitfalls
Using older TLS versions (1.0/1.1) or unencrypted connections, which can lead to lower trust scores from mailbox providers.
Failing to secure tracking or image domains with SSL, causing browser warnings and a negative user experience.
Relying solely on TLS for deliverability improvements without addressing other critical factors like email authentication.
Expert tips
Consider that while direct deliverability impact from TLS for MTA-to-MTA might be debated, it is a foundational security measure that signals legitimacy.
Remember that modern mailbox providers increasingly favor secure connections across the entire email journey, not just the initial send.
Ensure your DNS records are correctly configured for your sending subdomains to support proper authentication and TLS.
Marketer view
Marketer from Email Geeks says SSL is typically for HTTPS connections, not SMTP, where TLS encryption is used.
April 9, 2021 - Email Geeks
Marketer view
Marketer from Email Geeks says TLS for outbound emails, specifically STARTTLS, should be implemented, but there might not be a direct impact on deliverability.
Google and 
Microsoft. Maintaining a robust domain reputation requires a holistic approach to email security and best practices.
