How do I send Terms & Services emails to in-app users without disrupting deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Jun 2025
Updated 19 Aug 2025
7 min read
Sending mandatory Terms & Services (T&S) emails to a large base of in-app users, especially those not regularly engaged with your marketing communications, presents a unique challenge. Unlike promotional campaigns, these emails are often legally required, meaning you can't simply avoid sending them to unengaged users.
The core issue is balancing your legal obligations with maintaining a strong sender reputation. A large, sudden email send to an unengaged or dormant list can trigger spam filters, lead to high bounce rates, and increase spam complaints. This can quickly damage your domain and IP reputation, impacting the deliverability of all your subsequent emails, including critical transactional messages.
Navigating this requires a strategic approach that prioritizes deliverability without compromising compliance. I'll outline the steps and considerations for effectively reaching your in-app users with T&S updates while safeguarding your email program.
The unique challenge of mandatory transactional emails
The primary risk when sending T&S updates to a wide, potentially inactive audience lies in how mailbox providers (like Google and Yahoo) perceive your sending behavior. They monitor various signals to determine your sender reputation, including bounce rates, spam complaints, and engagement. If a significant portion of your T&S emails bounce (due to old or invalid addresses) or get marked as spam, it signals to ISPs that you might be sending unwanted mail, even if the content is mandatory.
It's crucial to understand that even legally mandated emails are subject to the same deliverability rules. While some regulations (like CAN-SPAM in the US) differentiate between transactional and marketing emails regarding unsubscribe requirements, mailbox providers still filter based on reputation and engagement. A high volume of sends to unengaged users can trigger spam traps, which are email addresses specifically designed to catch senders with poor list hygiene. Hitting these can lead to immediate blacklisting (or blocklisting) and severe deliverability issues, as detailed in our guide on spam traps. This is why proactive measures are essential.
The challenge intensifies when dealing with millions of recipients. A large, sudden email blast can overwhelm your sending infrastructure and be perceived as suspicious by ISPs, regardless of content. This can lead to throttling or temporary blocklists, delaying or preventing your critical messages from reaching the inbox.
Strategic preparation for large sends
Before hitting send, thorough preparation is paramount. This involves not just cleaning your list but also segmenting your audience and considering alternative communication methods.
Audience segmentation: Divide your in-app users into segments based on their recent engagement. Prioritize sending to your most active users first, then gradually move to less engaged segments. This gradual sending approach (often called email warmup) helps establish trust with mailbox providers and minimizes risk. It's a key strategy for sending to unengaged lists.
List hygiene: Even for mandatory emails, removing known invalid or problematic addresses from your list before sending is vital. High bounce rates can significantly harm your sender reputation.
Consider alternative channels: If email is not the only channel available, leverage in-app notifications, push notifications, or SMS for users who are primarily active within your application. This can reduce the reliance on email for users who may not check their email frequently or who have abandoned their email address. This is a common approach for legally mandated notifications.
Working closely with your Email Service Provider (ESP) or transactional email platform is also key. They often have specific strategies or dedicated IP pools for high-volume, mandatory communications that can help mitigate risks. Always check their Acceptable Use Policy (AUP) regarding such sends to ensure compliance.
Technical foundations and compliance
Robust email authentication is not optional, it's foundational for any email program, especially for critical transactional messages. Implementing SPF, DKIM, and DMARC properly signals to mailbox providers that your emails are legitimate and from an authorized source.
Content best practices
Clear subject lines: Use a clear, concise subject line that immediately indicates the email's purpose, for example, "Important Update: Terms of Service Changes".
Plain text version: Always include a plain text version of your email. Spam filters often flag emails that only have an HTML version.
No marketing content: Strictly avoid promotional elements. T&S emails are transactional. Adding marketing content can increase spam complaints and classify the email as commercial, subjecting it to different regulations.
Legal link: Provide a clear, direct link to the full Terms & Services document on your website.
A comprehensive understanding of DMARC, SPF, and DKIM is critical. SPF (Sender Policy Framework) specifies which mail servers are authorized to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) provides a way for senders to digitally sign outgoing email messages, allowing recipients to verify the authenticity of the message. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM, giving senders a way to tell receiving email servers how to handle emails that fail authentication. Setting up a DMARC policy, even a permissive p=none policy, is a strong signal of legitimacy.
This record instructs receiving mail servers to quarantine emails that fail DMARC authentication and sends forensic and aggregate reports to the specified email addresses. These reports are invaluable for identifying and resolving authentication issues. Regular DMARC monitoring is essential for ensuring your legitimate emails are properly authenticated and delivered.
Monitoring and adaptation
After sending your T&S emails, the work isn't over. Continuous monitoring of your deliverability metrics is essential to catch any potential issues early. Keep a close eye on your bounce rates, spam complaint rates, and open rates (if tracked). Most ESPs provide dashboards for this.
Before the send
Segment your list: Prioritize engaged users. Gradually increase volume to less active segments.
Validate email addresses: Remove old or invalid addresses to prevent bounces.
Monitor metrics: Track bounce rates, spam complaints, and inbox placement.
Address issues: Investigate high bounce or complaint rates and adjust sending strategy.
Risks
Damaged sender reputation: Leads to future emails landing in spam.
Blacklisting (or blocklisting): Your domain or IP being added to a blacklist (or blocklist).
Legal non-compliance: If emails don't reach recipients, you might not meet legal notification requirements.
Mitigation
Phased rollouts: Start with smaller, highly engaged segments.
ESP consultation: Work with your provider for high-volume sends.
If you encounter high bounce rates or spam complaints, it's crucial to act quickly. This could involve pausing sends to specific segments, further cleaning your list, or reviewing your email content. Remember, a single problematic send can have long-lasting effects on your email program, potentially leading to deliverability issues for all your emails.
For a deeper dive into the technical aspects of email deliverability and how to troubleshoot common issues, consider exploring resources like the M3AAWG document on sending mandatory emails best practices.
Views from the trenches
Best practices
Start by segmenting your user base, prioritizing your most engaged users for the initial send.
Always validate your email list before sending to reduce bounces and improve deliverability.
Ensure your email authentication (SPF, DKIM, DMARC) is properly configured and aligned.
Communicate with your Email Service Provider (ESP) in advance, especially for large volumes.
Consider using a dedicated subdomain for your transactional emails to isolate their reputation from marketing emails.
Keep the email content strictly transactional, avoiding any marketing or promotional elements.
Common pitfalls
Sending to an entire unsegmented list at once, especially a dormant one, can lead to high spam complaints.
Neglecting to clean your email list, resulting in high bounce rates and potential blacklisting (or blocklisting).
Failing to set up proper email authentication, which can cause emails to be marked as spam or rejected.
Assuming that because an email is mandatory, it bypasses deliverability rules or ESP Acceptable Use Policies.
Including marketing content in transactional emails, which can confuse recipients and trigger spam filters.
Not having a plain text version of your email, a common flag for spam filters.
Expert tips
For very large sends to potentially unengaged users, consider a phased rollout over several days or weeks.
Leverage in-app notifications or push alerts as a primary communication method if email is high-risk.
Continuously monitor your deliverability metrics and DMARC reports to identify and address issues promptly.
Maintain separate sending IPs or subdomains for transactional and marketing emails to protect critical communications.
If your volume is in the millions, discuss a dedicated sending plan with your ESP for specialized support.
Remember that ISP rules evolve; stay updated on changes from major providers like Google and Yahoo.
Marketer view
Marketer from Email Geeks says if the communication is truly mandatory and has zero marketing, there are specific actions to take. The number of recipients and available channels are key considerations.
2021-12-14 - Email Geeks
Expert view
Expert from Email Geeks says it is worth reviewing the M3AAWG best practices document for sending mandated emails, as it provides valuable guidance.
2021-12-14 - Email Geeks
Ensuring critical updates reach their audience
Sending Terms & Services emails to a large base of in-app users without disrupting deliverability is a significant challenge, but one that can be managed effectively with careful planning. By focusing on smart segmentation, robust authentication, clear content, and continuous monitoring, you can fulfill your legal obligations while protecting your sender reputation.
Remember, proactive engagement with your ESP and adherence to deliverability best practices are your strongest allies in ensuring your critical messages always reach their intended recipients. This approach not only ensures compliance but also fosters continued trust with your user base.
Google and 
Yahoo) perceive your sending behavior. They monitor various signals to determine your sender reputation, including bounce rates, spam complaints, and engagement. If a significant portion of your T&S emails bounce (due to old or invalid addresses) or get marked as spam, it signals to ISPs that you might be sending unwanted mail, even if the content is mandatory.
