What are the challenges and compliance requirements for sending email to SMS gateways?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 Jun 2025
Updated 19 Aug 2025
7 min read
Sending emails directly to SMS gateways might seem like a straightforward way to reach mobile users, but it's fraught with significant challenges and strict compliance requirements. What many don't realize is that this method of communication is increasingly discouraged and, in some cases, actively blocked by major carriers. It's not simply about formatting an email address correctly, such as 123456@txt.att.net, but understanding the intricate web of regulations and technical hurdles involved.
The landscape for email-to-SMS is rapidly changing. Key communication service providers, like Twilio SendGrid, have already announced (or are in the process of) blocking email-to-SMS gateway traffic for commercial use. This shift reflects broader industry standards and carrier requirements aimed at combating spam and enhancing security. For businesses relying on this method, it means adapting quickly or facing severe deliverability issues and potential legal repercussions.
This deprecation isn't arbitrary, it's a response to long-standing problems. The free email-to-SMS gateways offered by mobile carriers were never truly designed for high-volume or commercial messaging. They're often heavily filtered, leading to unreliable delivery, and they present significant security vulnerabilities, making it easy for malicious actors to spoof sender addresses and conduct smishing (SMS phishing) attacks. These issues have forced a move towards more controlled and compliant A2P (Application-to-Person) messaging channels.
The shifting landscape of email to SMS
For years, the simplicity of sending an email to a phone number's gateway address made it an appealing option for quick alerts or notifications. However, this convenience came with a hidden cost: poor deliverability and zero control over how carriers treated these messages. Unlike direct SMS solutions that operate over dedicated channels, email-to-SMS messages are treated like any other email, subject to the same rigorous spam filters and blocklist (or blacklist) checks that apply to regular emails. Many carriers, including AT&T, Verizon, and T-Mobile, have either shut down or severely restricted these free gateways.
Email to SMS gateway deprecation
Major carriers are deprecating or shutting down their traditional email-to-SMS gateways due to escalating spam, security risks (like smishing), and the push towards more regulated A2P messaging. This means messages sent via these methods are increasingly failing to deliver or experiencing significant delays. Businesses should transition to dedicated SMS APIs or certified messaging platforms.
The primary drivers for this change are twofold: controlling unsolicited messaging (spam) and enhancing the security of text communications. Email's open nature, where the sender's address can be easily forged, made it a prime target for abuse. By shifting to more controlled environments, carriers can enforce stricter sender verification and content filtering, ensuring a more reliable and trustworthy communication channel for legitimate businesses and users alike.
Compliance complexity: navigating regulations
Navigating the regulatory landscape for text messaging is far more complex than for email. While email has regulations like CAN-SPAM and GDPR, SMS messages fall under even stricter rules, particularly in the US with the Telephone Consumer Protection Act (TCPA) and in Europe with the GDPR. These laws mandate explicit consent, clear opt-out mechanisms, and strict adherence to content and timing guidelines. For example, the FCC maintains a list of wireless domain names to which unsolicited emails should not be sent due to their nature as wireless devices.
Email compliance (e.g., CAN-SPAM, GDPR)
Easier consent: Implied consent can sometimes be acceptable, though explicit opt-in is best.
Clear sender ID: Sender information must be accurate and identifiable.
Opt-out mechanism: Easy and functional unsubscribe link required.
Less stringent: Fewer content restrictions and timing rules.
SMS compliance (e.g., TCPA, CTIA, GDPR)
Express written consent: Strictly required, often with double opt-in. See SMS marketing rules.
Clear disclosure: Purpose and frequency of messages must be clear.
Easy opt-out: Keywords like STOP, END, CANCEL must function.
Heavy penalties: Non-compliance can lead to substantial fines per message.
The burden of proof for consent falls entirely on the sender. If a recipient claims they didn't opt in, you must be able to produce verifiable records of their express consent. This is a far higher bar than typical email marketing and can be extremely challenging if you are relying on an archaic email-to-SMS setup without robust consent tracking.
Furthermore, if you are sending via an email-to-SMS gateway and the phone number provided by a user does not actually belong to them, the legal and financial ramifications for you are much more significant than for a standard email. This necessitates a proactive and defensive approach during the user signup process to verify ownership and consent.
Technical hurdles and deliverability pitfalls
Beyond compliance, the technical aspects of email-to-SMS gateways pose significant deliverability challenges. These gateways often experience issues like delayed delivery due to network congestion, compatibility problems across different carrier networks, and a general lack of visibility into message status. Unlike dedicated SMS APIs that provide delivery receipts and robust error handling, email-to-SMS offers minimal feedback, leaving you blind to whether your messages are reaching their intended recipients.
Challenge
Impact
Why it happens
Carrier blocking
Messages undelivered
High spam complaints, lack of A2P registration.
Lack of security
Smishing and spoofing risks
Email's open 'From' address vulnerability.
Inconsistent formatting
Messages appear garbled
Different carrier gateway requirements.
No delivery receipts
Unable to verify delivery
Email protocol doesn't support SMS-specific statuses.
The very nature of how these gateways work makes them prone to deliverability issues. They are not built for robust, commercial use, and mail servers and carriers will preemptively suppress (blocklist) domains frequently sending to these gateway addresses. Even with explicit opt-in, achieving reliable delivery at scale through these channels is extremely difficult.
Furthermore, the lack of transparency means you often don't know why a message failed. Was it a network issue, carrier filtering, or a compliance flag? This makes troubleshooting and improving deliverability rates incredibly difficult, leading to frustrated recipients and missed communications, especially for time-sensitive notifications.
Best practices for reliable SMS delivery
Given the challenges, the best practice is to move away from email-to-SMS gateways for any critical or commercial messaging. Instead, leverage dedicated SMS API providers or communication platforms that are built specifically for A2P messaging. These services offer direct connections to carriers, ensuring higher deliverability rates, proper compliance handling, and robust reporting.
Transitioning to dedicated SMS platforms
Use SMS APIs: Integrate with SMS service providers for reliable, compliant A2P messaging.
Obtain consent: Always get explicit, verifiable opt-in from recipients before sending. This is crucial for SMS compliance.
Clear opt-out: Provide clear and easy ways for users to stop receiving messages.
Monitor delivery: Utilize reporting features to track deliverability and diagnose issues.
Verify numbers: Implement phone number verification at signup to prevent sending to wrong recipients.
Adhering to best practices for consent and sender identification is paramount. This includes implementing a double opt-in process for SMS subscriptions, clearly stating the purpose of messages, and providing an unambiguous way for recipients to opt out at any time. Investing in a robust SMS platform is not just about compliance, it's about safeguarding your brand's reputation and ensuring your messages reliably reach your audience.
Ultimately, while the idea of sending email to SMS gateways might seem appealing for its perceived simplicity, the reality is that it's an outdated and unreliable method. For any serious business communication, especially anything transactional or marketing-related, direct SMS solutions are the only way to ensure deliverability, compliance, and maintain a positive sender reputation. Don't risk emails going to spam or text messages failing to deliver due to these deprecated methods.
Views from the trenches
Best practices
Always obtain explicit, verifiable consent for SMS messages, and be prepared to prove it.
Use dedicated SMS API services for commercial or critical messaging instead of email-to-SMS gateways.
Implement phone number verification at the point of signup to ensure numbers belong to the opting-in user.
Common pitfalls
Relying on free email-to-SMS gateways, which are increasingly blocked and unreliable for business communications.
Failing to capture and retain clear proof of consent, leading to compliance violations.
Not providing clear and functional opt-out mechanisms for SMS recipients.
Expert tips
Carrier-provided email-to-SMS gateways are heavily filtered, even for legitimate opt-in messages, leading to low deliverability.
The FCC maintains a list of wireless domain names to which unsolicited email should not be sent.
ESPs often preemptively suppress domains associated with email-to-SMS gateways due to high blocking rates.
Expert view
Expert from Email Geeks says sending emails to telco SMS gateways is very problematic because the FCC has extremely tight constraints on such messages, and email service providers often preemptively suppress these domains.
2024-03-01 - Email Geeks
Expert view
Expert from Email Geeks says operator-provided gateways are heavily filtered, meaning even opt-in emails are unlikely to be delivered at volume, with some legitimate non-profits experiencing permanent blocks.
2024-03-05 - Email Geeks
Moving forward with confidence
The challenges and compliance requirements for sending email to SMS gateways are formidable and continually evolving. As carriers move to shut down these services, relying on them for your communications is no longer viable or advisable. The shift towards regulated A2P messaging is a clear signal that the industry demands higher standards of consent, security, and deliverability.
To ensure your messages reach their intended recipients and your business remains compliant, it's essential to transition to professional SMS solutions. These platforms offer the reliability, visibility, and compliance features necessary to navigate the complex world of text messaging effectively. Prioritize explicit consent and choose a dedicated SMS provider to maintain strong email deliverability and avoid costly penalties.
