What to do when experiencing issues sending email to SMS texts via ATT?
Matthew Whittaker
Co-founder & CTO, Suped
Published 4 Jul 2025
Updated 16 Aug 2025
7 min read
Dealing with email-to-SMS delivery failures, particularly when sending messages to AT&T recipients, can be incredibly frustrating. I've encountered numerous instances where businesses and individuals face sudden interruptions, often receiving cryptic error messages like '550 5.2.0 - Internal error' when attempting to send emails to phone@mms.att.net or phone@txt.att.net addresses. This specific error often indicates an issue on the receiving end's gateway.
While email-to-text was once a convenient feature for various alerts and communications, its reliability has been diminishing. This is partly due to the nature of email gateways, which were not designed for the same robust deliverability as direct SMS services. Furthermore, carriers like AT&T are increasingly deprecating these services.
This guide outlines the reasons behind these issues, especially with AT&T, and provides practical steps and alternatives to ensure your critical messages reach their intended recipients.
Understanding the recent changes
The most significant factor affecting email-to-SMS deliverability to AT&T devices is the announced shutdown of their service. AT&T officially announced that their email-to-text and text-to-email services will be discontinued as of June 17, 2025. This means that after this date, sending emails to @txt.att.net or @mms.att.net addresses will no longer function.
Even before the complete shutdown, AT&T's email-to-SMS gateways were not designed for high-volume or commercial use. They were primarily intended for occasional personal messages. This often led to inconsistent deliverability, with messages being delayed, dropped, or bounced back without clear explanations. Many users reported a sudden cessation of service, even for messages that previously delivered without issues.
The reason for phasing out these services is largely tied to evolving communication standards, security concerns, and the rise of more dedicated messaging solutions. Email-to-SMS gateways are more susceptible to spam and abuse, making them less desirable for carriers to maintain. This transition underscores the importance of using robust and compliant methods for sending critical SMS communications.
Understanding the problem
Email-to-SMS gateways were convenient but not built for scale or security, often leading to inconsistent delivery. Senders might see generic error messages or no delivery notifications at all.
Carrier limitations
Carriers like AT&T are actively moving away from supporting these gateways. This means that even if you've had success in the past, it's increasingly likely to fail or be phased out, as this functionality is being eliminated entirely.
Common issues and diagnostic steps
If you're still experiencing issues before the June 2025 shutdown, or for other general email delivery concerns, several factors could be at play. The `550 5.2.0` internal error I mentioned earlier often points to an issue on AT&T's side related to their gateway processing your message. This could be due to volume limits, content filtering, or transient system errors.
For general email troubleshooting, always start by verifying the basics. Is the recipient's phone number correct? Are you using the proper gateway address for AT&T? Although the service is ending, historical issues also included messages being too long, containing problematic content, or hitting AT&T's spam filters. It's also worth checking if your sending IP or domain is on any email blocklist or blacklist, which can affect all your email deliveries.
If you receive a delivery status notification (DSN) with an error code, this provides crucial information. The example error 550 5.2.0 often means a permanent failure due to an internal server error on the recipient's side, as seen in user reports. If no DSN is received, the message might be silently dropped, making it harder to diagnose. In such cases, contacting AT&T support directly can sometimes provide clarity, although their support for these gateways is limited.
Example of a common email-to-SMS bounce message
Diagnostic information for administrators:
Generating server: BY5PR03MB5267.namprd03.prod.outlook.com
{phone}@mms.att.net
Remote Server returned '550 5.2.0 <x@y.com> - YET8oD0cbiOewYET8op5DU - Internal error'
Alternatives to email-to-SMS
Given AT&T's impending shutdown of email-to-SMS, the most practical solution is to transition to dedicated SMS messaging platforms. These services are built for reliable text message delivery and offer far more control and features than email gateways ever did. They bypass the inconsistencies and limitations inherent in email-to-SMS, ensuring your messages reach recipients promptly.
Dedicated SMS platforms leverage direct connections to mobile carriers, which translates to higher deliverability rates, proper compliance with messaging regulations (like TCPA and CAN-SPAM), and detailed delivery reports. This is crucial for critical communications where timely receipt is paramount, such as alerts for internal teams, two-factor authentication codes, or urgent customer notifications.
Exploring these alternatives now, well before the June 2025 cutoff, will allow for a smooth transition without disruptions to your communication flows. Many providers offer APIs that integrate seamlessly with existing systems, providing a robust and scalable solution for all your SMS needs. This proactive approach will help you avoid future delivery failures and maintain reliable communication channels.
Email-to-SMS gateways
Reliability: Inconsistent delivery due to carrier policy changes and spam filters.
Compliance: Difficult to ensure opt-in and adhere to messaging regulations like TCPA.
Features: Limited functionality; basic text only, no delivery reports or analytics.
Future: Being deprecated by major carriers, including AT&T.
Dedicated SMS platforms
Reliability: High deliverability rates through direct carrier connections and robust infrastructure.
Compliance: Built-in features for managing opt-ins, opt-outs, and adhering to strict messaging regulations.
Features: Advanced capabilities like delivery reports, analytics, two-way messaging, and bulk sending.
Future: The standard for reliable and scalable business messaging.
Best practices for SMS deliverability
Even when using dedicated SMS platforms, maintaining good sending practices is crucial for ensuring your messages land in the inbox. Much like email, SMS deliverability is affected by sender reputation and compliance. Neglecting these can lead to messages being blocked, filtered, or delayed by carriers.
First, always ensure you have explicit consent (opt-in) from recipients before sending any SMS messages. This is a fundamental requirement for compliance and avoids issues like spam complaints or carrier violations. Provide clear instructions for opting out, and honor those requests promptly. Sending unwanted messages can quickly lead to your number or sender ID being blocklisted by carriers or reported to authorities, severely impacting your ability to deliver future messages.
Secondly, pay attention to content. Avoid sending messages that are overly promotional, contain suspicious links, or mimic spam. Keep your messages concise and relevant. Carriers employ sophisticated filters to detect and block (or blacklist) suspicious SMS traffic. Understanding these nuances can significantly improve your SMS deliverability rates and help prevent messages from going to spam, whether via email or SMS. Regularly monitor your delivery reports to identify any issues quickly.
Views from the trenches
Best practices
Always obtain explicit opt-in consent before sending SMS messages to avoid compliance issues and maintain a good sender reputation.
Use dedicated SMS API services or platforms for bulk messaging instead of unreliable email-to-SMS gateways, especially given AT&T's shutdown.
Monitor delivery reports and bounce rates closely to quickly identify and address any deliverability issues with SMS carriers.
Keep SMS content clear, concise, and relevant to avoid triggering spam filters and ensure messages are well-received by recipients.
Common pitfalls
Continuing to rely on email-to-SMS gateways, particularly for AT&T numbers, will result in complete delivery failure after June 2025.
Sending SMS messages without proper opt-in consent, leading to high complaint rates, blocklists (blacklists), and potential regulatory fines.
Ignoring bounce or error messages from email-to-SMS gateways, preventing timely diagnosis and resolution of delivery problems.
Using generic, untraceable sender IDs, which makes it difficult for recipients to identify your messages and increases the likelihood of being marked as spam.
Expert tips
Consider segmenting your audience and tailoring SMS content for higher engagement rates, similar to best practices for email marketing.
Implement two-way SMS communication where appropriate to allow recipients to easily respond, improving engagement and feedback loops.
For critical alerts, implement fallback mechanisms, such as email or voice calls, if SMS delivery fails, ensuring messages are always received.
Regularly audit your contact lists to remove invalid or inactive numbers, which can improve overall SMS campaign efficiency and deliverability.
Marketer view
Marketer from Email Geeks says they recently encountered the '550 5.2.0 Internal error' when sending email to SMS texts from Office 365, indicating a possible internal issue on the AT&T side.
2022-09-18 - Email Geeks
Marketer view
Marketer from Email Geeks notes that some AT&T email-to-text gateways are not intended for bulk use and are largely unsupported, which can cause significant delivery challenges.
2022-09-18 - Email Geeks
Ensuring your messages get through
While encountering email-to-SMS delivery issues with AT&T can be perplexing, especially with the 'internal error' messages, the underlying cause is often the deprecation of these legacy gateways. The shift towards dedicated SMS solutions by carriers is a clear signal that it's time to adapt your communication strategy.
By understanding these changes, implementing best practices for SMS deliverability, and proactively transitioning to robust SMS platforms, you can ensure your critical text messages continue to reach their intended audience reliably. This move not only resolves current frustrations but also future-proofs your messaging strategy against evolving carrier policies and technological advancements.
