Sometimes SMS messages don’t arrive as expected. This guide offers practical tips to improve deliverability and ensure important information reaches your participants.
Qondor uses Twilio, a trusted global SMS provider, to send messages from projects. While most messages are delivered instantly, you might notice that some are delayed or blocked. This is usually due to rules or limitations set by mobile networks and phone providers, and not by Qondor itself.
WHY A SMS MIGHT NOT ARRIVE
Most SMS messages go through without issue, but when they don't, it’s usually due to one of the following reasons:
Incorrect phone number formatting
Flagged or rejected by mobile operators due to links, emojis, or content
Unsupported sender types (e.g. alphanumeric* names in some countries)
Missing opt-in or consent from recipients
Technical delivery issues (rare, but possible)
*alphanumeric: means a combination of letters (A–Z) and numbers (0–9).
To help you send reliable messages, we've compiled tips and best practices, plus some technical insight into how SMS works in Qondor.
MOST COMMON ISSUES AND HOW TO PREVENT THEM
Cause | What it means | How to prevent it |
Incorrect phone number format | The number is not in standard format for international telephone numbers (E.164** format) and is rejected by Twilio. | Always use standard format (e.g. country code |
Operator filtering | Message content is flagged as suspicious by mobile operators (spam filters). | Avoid public shortener sites (e.g. bit.ly), emojis, special characters, and “spammy” text. |
Blocked sender name | Some countries don’t allow alphanumeric sender names. | Use a compliant sender or rely on Qondor’s fallback logic for unsupported countries. |
Missing opt-in | The recipient hasn’t explicitly agreed to receive SMS, triggering filtering. | Only send SMS to users who’ve given clear consent. Respect opt-outs. |
Technical issues | Network errors, timeouts or Twilio API problems during sending. | Qondor automatically retries failed sends up to 2 times. Check Communication Center. |
**E.164 = the standard format
A plus sign (+), the country code, and the full number without spaces or leading zero. For example, a UK phone number in this format would look like this --> +447911123456).
5 BEST PRACTICES TO IMPROVE SMS DELIVERABILITY
1. Use correct phone number format
Always use the standard format for international telephone numbers (E.164 format**) when adding participant phone numbers.
Avoid using spaces, brackets or dashes in numbers.
❗Numbers with the wrong format are rejected immediately and the message won't be delivered.
💡 Tip: Export participant lists from Qondor and validate numbers before sending bulk SMS.
2. Avoid URLs that are not from Qondor
We recommend using URLs that are generated by Qondor, as they are whitelisted and trusted by us.
If you must use external links, avoid public shortener sites (e.g. site like bit.ly), which are often blocked by mobile carriers.
3. Watch out for emojis and special characters
Qondor does not officially support emojis. However, it may still be possible to paste them into an SMS message. If you do, be aware that emojis and special symbols can make your SMS more expensive and harder to deliver.
Even a single emoji (like 😊 or ❤️) will change how your SMS is encoded, cutting the maximum length per message from 160 characters down to 70.
Some emojis, such as flags or combined emojis (👨👩👧), can take up the space of two or more characters, even though they appear as a single symbol.
Character type | Max per message | What to know |
Standard letters (A–Z) | 160 characters | ✅ Safe and efficient |
æ, ø, å | 160 characters | ✅ Supported (may use a little more space) |
Emojis (😊, ❤️, 👨👩👧) | 70 characters | ❌ Lowers character limit significantly |
4. Monitor your message status
Use the Communication Center in Qondor to:
Check if messages were delivered, failed, or undelivered.
See delivery status and any error messages.
Resend a message if needed.
💡 Open your project’s Communication Center and filter by SMS to see individual message details.
📝 More info: Communication Center
5. Use a recognisable SMS sender name
Qondor lets you customise the SMS sender name (for example, your customer's name or event name). However, the most reliable option is to use your company name, since this is whitelisted and less likely to be blocked.
Preferably use your company name as sender name for the SMS (default).
Not all countries support alphanumeric sender names.
If unsupported, Qondor will use a fallback number registered with Twilio.
Replies sent to fallback numbers will go to Twilio’s inbox, not back to Qondor.
📝 More info: Custom SMS sender names