Overview
Customers typically already have an extension scheme in place. When building out a new domain, we should strive to follow the customer’s existing extension numbering scheme as closely as possible to avoid confusion and support smoother adoption.
Recommended User Extension Ranges
When creating a new domain, use the following extension schemes for user extensions:
- 100–998
- 1000–8999
- 10000–199999
- 100000–199999
These ranges are guidelines. If the customer already has a numbering plan in place, prioritize matching their existing structure whenever possible.
Important
These ranges are guidelines. If the customer already has a numbering plan in place, prioritize matching their existing structure whenever possible.
Reserved Extensions (Do Not Use for User Extensions)
The following extensions are reserved and should not be assigned to individual users.
- 111
- 211
- 311
- 411
- 511
- 611
- 711
- 811
- 833
- 911
- 933
- 999
- 5000 & 5001
- 9000–9999
x11 numbers are set to only show the outbound Caller ID on X11 numbers. They must show outbound Caller ID and PSAP (or location) information.
Call Flow Extension Guidelines
Use the following extension ranges when building call flows and system features:
| Feature / Object | Recommended Extension Range |
|---|---|
| Call Queues | 8500–8999 |
| Auto Attendants | 8500–8999 |
| Conference Lines | 8500–8999 |
| Call Parks | 9000–9999 |
| Paging Units (Snom, CyberData) | 7777 & 8888 (most common) |
Troubleshooting
User extension conflicts with a system feature
- Verify the extension is not in the reserved list (e.g., 911, 933, 999, 9000–9999, 5000/5001).
- Confirm call flows (queues/auto attendants/conferences) use 8500–8999 and call parks use 9000–9999.
Features not working consistently across devices
- Confirm all devices are assigned to the same server (USW, USC, or USE) for the entire account.
- If there are multiple physical locations, validate the selected server is closest to the main location.
FAQ
Should we always use the recommended ranges exactly as listed?
No. The priority is to match the customer’s existing extension scheme as closely as possible. The ranges above are the standard starting point for new domains.
Why can’t we assign 9000–9999 to users?
That range is reserved for Call Parks and other system behaviors. Assigning it to users can create conflicts and unpredictable routing.
If you need additional assistance, please contact Crexendo Support at 855-211-2255 or email us at support@crexendo.com — our team is happy to help!