Native Fax
Considerations with Native Fax
The VoIP Help Page Team·3 min read·Last updated: March 14, 2026
This article outlines important considerations and limitations when using native fax services, including email integration, file size restrictions, transmission times, and caller ID behavior.
This document contains a list of things to consider with Native Fax
| Consider | Description |
|---|---|
| Multiple emails per account | Multiple emails may be delivered to, however, only the first email on the account will be allowed to send fax via email.<br>If multiple users are to use the fax account, the recommended method is to use a Shared Mailbox within your email provider to achieve this functionality. |
| Migrate sent/received faxes to a new user | You can move or re-purpose the fax account to another user but you're not able to move the sent/received faxes for the DID to the new user. The use case for the ability to migrate the faxes to a new user is when the current user in the OMP has a change of role in the company and a new user will be filling up the role. You want to retain all faxes for the new user instead of recreating the OMP account. |
| Fax Call History | Sent and Received faxes will not show up in the call history |
| ATA/Email Faxes | Faxes sent from an ATA device and via email will not show in the sent folder of the user. |
| One-To-One mapping | Phone number can only be assigned to a single user. Similarly, a user cannot have multiple fax numbers assigned to it. |
| File Size Restrictions | Faxes are limited to a 100mb file size, anything larger will fail to send.<br>Note: When using Fax via Email (Native Fax: Send a Fax From Email (helpjuice.com)) the file size restriction is 10MB. |
| Fax Transmission Time | Fax transmissions generally take 60 to 120 seconds per page. However, transmission time can increase significantly based on document content. Dark images, heavy use of black, graphics, logos, and dense text require more data processing, leading to longer send times—especially for multi-page faxes, where 10-15 minutes or more is expected for complex documents. To reduce transmission times, use text-only documents whenever possible, avoid unnecessary graphics or logos, and ensure pages are clean with minimal dark or shaded areas. If a simple 1-2 page text fax experiences excessive delays or failures, further investigation may be needed. |
| Outbound Fax Caller ID | It is possible to modify the ANI per account since this does not matter in our vendor's software. However, they have seen instances where phone carriers will block unknown ANIs. So, if you are trying to use a number that is not real or not part of your inventory, your carrier could decline the call. |
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