RCS vs SMS vs MMS
RCS, SMS, and MMS are all mobile messaging channels, but they differ significantly in capabilities, user experience, tracking, and performance measurement.
This article explains how each channel works, when to use them, and what to expect when comparing performance.
Overview
Use SMS for text-only messages, MMS when an image or GIF helps explain your message, and RCS for branded messages with read receipts and interactive content.
Once an RCS agent is active in a country, Klaviyo sends RCS to capable recipients there and uses the SMS or MMS fallback for other recipients. Learn more about getting started with RCS.
Basic RCS and Single RCS are pricing categories based on message content and destination. In the RCS editor, you choose Text only or Rich cards. See RCS pricing for the regional differences.
SMS | MMS | Basic RCS | Single RCS | |
Delivery Receipts | Yes | Yes | Yes | Yes |
Read Receipts | No | No | Yes, when the recipient has read receipts enabled | Yes, when the recipient has read receipts enabled |
Click Tracking | Yes (via shortened links) | Yes (via shortened links) | Yes | Yes |
Encryption | No | No | Yes, in transit; not end-to-end encrypted | Yes, in transit; not end-to-end encrypted |
Character Limit | 160 for a single segment (70 with non-GSM characters such as emojis). Longer messages use multiple segments, up to 1,600 characters in Klaviyo. | 1,600 | Up to 3,072 in the US and Canada, billed in 160-character segments; up to 160 per message elsewhere | 3,072 for text-only messages priced as Single RCS; up to 200 per card title and 2,000 per card description |
Media | No | Yes, but with size restrictions (one media file per message up to 600 KB) | No | High-quality media: 1 attachment per rich card, with up to 10 cards per message. Image uploads can be up to 10 MB; the total message limit is 100 MB. |
Interactive Elements | No | No | Partial for US and Canada (quick replies and links that open in a browser) | Yes (cards, buttons, quick actions etc.) |
Location Sharing | No | No | No | Yes not yet supported in Klaviyo |
Payment & App Integrations | No | No | Yes | Yes not yet supported in Klaviyo |
Device Reach | All mobile phones with a network connection | MMS-capable phones on supported networks; Klaviyo availability also depends on country and sending number | RCS-capable devices only (Android 5.0+ or iOS 18+ on supported networks) | RCS-capable devices only (Android 5.0+ or iOS 18+ on supported networks) |
Verified Senders | No | No | Yes | Yes |
Branded Senders | Partial (for alphanumeric senders only) | No | Yes (company logo & info page) | Yes (company logo & info page) |
Message history on the recipient’s device | Yes | Yes | Yes | Yes |
Throughput | Uses SS7 signalling via SMSCs, limited by payload and latency | Uses SS7 signalling + WAP/HTTP for multimedia, typically slower than SMS | Uses modern IP networks (LTE, 5G, Wi-Fi) for fast, efficient delivery | Uses modern IP networks (LTE, 5G, Wi-Fi) for fast, efficient delivery |
Performance Metrics
When comparing performance across channels, it is important to understand structural differences in how performance metrics are measured.
Delivery rates
When comparing delivery performance across channels, it is important to understand how delivery is reported differently for SMS and RCS.
SMS delivery reporting
With SMS, carriers do not always return a delivery receipt or a failure event. After a message is sent, the possible outcomes are:
- A confirmed delivery receipt
- A failure event, or
- No explicit event is returned
In a small percentage of cases (less than 3%), no explicit delivery or failure event is returned. Klaviyo can count these SMS messages as delivered after a provider-specific waiting period. These are assumed deliveries, not confirmed delivery receipts.
RCS delivery reporting
RCS delivery reporting uses explicit delivery and failure events. A delivery attempt can result in:
- A confirmed delivery receipt, or
- A failure event
Klaviyo does not assume that an RCS message was delivered when a delivery receipt is missing.
RCS failure categories
- Device unreachable - Delivery was attempted for up to 24 hours without success. After this window, the message is marked as failed and categorized as 'Device unreachable'.
- Device not RCS capable - The recipient’s handset cannot receive RCS. This may be due to RCS being disabled, an unsupported network, or an unsupported operating system. The message is marked as failed and categorized as 'Device not RCS capable'.
If a failure is due to the device being incapable of receiving RCS, Klaviyo updates the phone number's capability information so that future text messages use the SMS or MMS fallback while the recipient is not RCS-capable.
Click rates
Note: if you have chosen not to exclude bot clicks from your reporting, RCS click rates may appear lower than SMS click rates. RCS experiences significantly fewer bot clicks due to how links and clicks are handled within the RCS ecosystem. As a result, RCS click rates are generally more reflective of genuine human engagement.
Removing bot clicks in reporting
Klaviyo recommends excluding bot clicks from both your account’s reporting data and attribution calculations. This helps prevent automated link scans from inflating engagement reports or receiving credit for conversions. Learn how to remove bot clicks.
Note: Even with bot filtering enabled, not all bot traffic can be removed from SMS reporting. As a result, SMS click rates may appear higher than RCS.
What to compare instead
Rather than comparing raw click rates, we recommend focusing on:
- Conversion rate (placed order rate)
- Klaviyo attributed value (KAV)
- Revenue per recipient
These metrics better reflect real customer behavior and true business impact.
Opt-outs
Opt-outs are separate from delivery failures and are handled differently across SMS and RCS.
SMS opt-outs
An SMS opt-out occurs when a recipient:
- Replies with a recognized keyword such as STOP to a number that supports replies, such as a toll-free number, long code, or short code, or
- Uses an unsubscribe link, including in messages from alphanumeric sender IDs that do not support replies
In both cases:
- The recipient’s text messaging marketing consent is removed
- Future RCS, SMS, and MMS marketing messages cannot be sent unless the recipient opts in again
Important: If a recipient blocks a phone number directly on their device, this does not generate an event back to Klaviyo. Messages may continue to be technically delivered but will not be seen by the recipient.
RCS opt-outs
With RCS, recipients can opt out in two primary ways:
- Replying with STOP (or equivalent), or
- Clicking “Block this sender” within the RCS agent information screen
In both cases:
- The recipient’s text messaging marketing consent is removed
- Future RCS, SMS, and MMS marketing messages cannot be sent unless the recipient opts in again
Important: If a recipient has iOS Unknown Senders filtering enabled and has not marked your RCS agent as known, messages may be routed to the Unknown Senders inbox and may not be actively seen. For more information, see Understanding Unknown Senders filtering on iOS and how it affects RCS.