Adaptive AI Knowledge Base
Phone, SMS & Calling
This article explains the file size limits of attachments for both SMS and email sent through the platform. It also introduces a powerful enhancement — Attachments Made Easy in Conversations — which lets you send larger files effortlessly via Media Library links and auto-generates video thumbnails to boost engagement.
Key Benefits of Understanding File Size Limits
Knowing attachment limits helps you avoid failed deliveries and ensures your emails and messages are optimized for deliverability and engagement.
- Prevents delivery issues caused by large files
- Ensures compliance with MMS and email provider rules
- Simplifies file handling using the built-in Media Library
- Reduces manual effort and reliance on third-party file hosting
- Reduces manual workarounds like compressing or hosting files externally.
- Speeds up the attachment process with direct device uploads.
- Improves engagement by making emails more visually appealing and interactive.
- Ensures smooth delivery across SMS and email by auto-managing limits.
SMS Attachment Size Limits
SMS messages can only contain text. To include attachments like images, videos, or audio files, you must use MMS, which is supported differently depending on the phone number type and carrier. If you're attaching a file to an SMS, it is automatically converted to an MMS. The following file types are supported for MMS:
Some file types like MP3, MP4, and PDF may work depending on the carrier and device. You can also check out Adaptive AI Phone’s list of supported media types here: Adaptive AI Phone Supported File Types.
The recommended best practice is to keep MMS attachments under 500 KB to ensure successful delivery across all carriers.
Carrier | Long Code MMS | Toll-Free MMS | Short Code MMS
AT&T* | 1.0 MB | 0.6 MB | 0.6 MB
T-Mobile | 1.5 MB | 0.6 MB | 1.0 MB
Verizon | 1.0 MB | 0.6 MB | 1.2 MB
As of October 2022, Toll-Free numbers support MMS. Before that, they supported SMS only.
Message Type | Supports MMS? | Recommended Max Size
Long Code (10DLC) | Yes | ~500 KB – 1 MB
Short Code | Yes | Up to 5 MB
Toll-Free | Yes (Since Oct 2022) | Up to 5 MB
Email Attachment Size Limits
Attachment limits for email depend on the email provider used. Exceeding these limits can cause emails to bounce or be undeliverable.
The platform's email composer allows up to 20 MB in attachments. Files above this size will be automatically uploaded to the Media Library and sent as clickable links.
Email Provider | Max Attachment Size
Gmail | 25 MB
Yahoo Mail | 25 MB
Outlook.com | 10 MB
Adaptive AI Email | 25 MB
How to Upload Attachments in Conversations
Uploading files directly in the Conversations composer has been made easier and more flexible with the new attachment workflow. Whether you're sending an SMS or an email, you can now upload files from your device or choose from your Media Library — all from within the message composer. This process eliminates the need to manually compress files or use third-party hosting platforms, streamlining your workflow and improving the customer experience. Here is a step-by-step process for uploading or attaching files.
To begin, open a conversation under the Conversations tab and click the three-dot icon (•••) in the message composer.
After clicking the three-dot icon, select “Attach Files”. You'll see two options:
If the file exceeds 20 MB (for email) or any size for SMS, the platform will automatically upload it to the Media Library and insert a clickable link into your message.
This ensures that your message is delivered without hitting size limits.
Video Uploads Get Auto-Generated Thumbnails. When uploading a video file through the Media Library, the platform will automatically generate a GIF thumbnail to be shown in your email, making your message more engaging and clickable.
Paste Attachments from Clipboard
Instead of opening the attachment menu, you can attach files by pasting them.
- 1Copy a supported file or image on your computer.
- 2Click inside the message composer in Conversations.
- 3Press (Windows) or (Mac), or right-click and.
The pasted file attaches instantly to the current message and respects the same size limits and media-handling rules described above.
How to Send Larger Files
- Upload directly via the email/SMS composer.
- Files larger than 20 MB are auto-hosted via the Media Library and inserted as links.
- Use cloud hosting only if needed outside the platform.
- Add videos via the Media Library for interactive thumbnails.