Overview

Sometimes, SMS messages you send may be marked as "delivered" but still don't appear on the recipient’s phone. One common cause is that the recipient’s mobile device has blocked your sending number, either manually or automatically.

Why Do Phones Block Numbers?

Mobile phones allow users to block phone numbers manually, and some devices may also auto-block suspected spam senders based on user settings or spam detection features.

Common reasons a number may be blocked:

  • The recipient accidentally added your sending number to their block list

  • They mistook a legitimate message for spam or promotional content

  • They received repeated similar messages and found them a nuisance

  • Your number is shared with other users who have sent nuisance messages to the recipient

When a number is blocked on a mobile device, messages are silently filtered and discarded. The sender receives no bounce-back or error; the message shows as delivered in your logs, but the recipient never sees it.

What You Might See

When this happens, you may notice the following:

  • The system logs show the message as "delivered"

  • The recipient claims they never received the message

  • Messages continue to show as delivered but are not acknowledged by the recipient

This mismatch can be confusing, but it often points to the recipient’s device filtering out messages from your sending number.

Best Fixes

There are two ways to resolve this issue:

Option 1: Change the Sending Number

You can send messages from a different phone number or short code.

This may be technically difficult, add additional cost, and could affect mobiles that are familiar with your current sending number.

Option 2: Ask the Recipient to Unblock Your Number

The most straightforward solution is to ask the recipient to check their phone’s blocked number list and remove your sending number if it appears there.

Here’s how to do that:

For Android Users

  1. Open the Phone or Messages app.

  2. Tap the three-dot menu (⋮) in the top-right corner.

  3. Go to Settings > Blocked numbers (or Spam & blocked depending on the device).

  4. Look for your sending number in the list.

  5. Tap Unblock if it's listed.

For detailed steps, refer to Google’s official guide:
🔗 Block or unblock a number - Google Help

For iPhone Users (iOS)

  1. Open the Settings app.

  2. Scroll to and tap Phone, Messages, or FaceTime.

  3. Tap Blocked Contacts.

  4. Look for your sending number in the list.

  5. Swipe left on the number and tap Unblock.

For detailed steps, see Apple’s support page:
🔗 Unblock a phone number or contact - Apple Support

Summary

If SMS messages show as delivered but don’t reach the recipient, the number may be blocked on their mobile device. You can:

  • Change your sending number (if feasible), or

  • Ask the recipient to remove the block on their phone using the above steps.

This is a device-level issue, so it’s important to coordinate directly with the message recipient when resolving this type of delivery problem.