FAX Won't Open? Convert to SUN Instantly
Fast, instant FAX to SUN conversion. No signup required. Just drop your .fax file and get .sun in seconds.
Batch Settings
About FAX to SUN Conversion
Dealing with a FAX file that won't open on your device? You're not alone — FAX compatibility issues are one of the most common reasons people search for a file converter. FAX is a widely used file format.
The fix is simple: convert your FAX to SUN. SUN is a widely used file format. This conversion lets you convert between formats quickly, solving the problem in seconds rather than hours of troubleshooting.
Converting FAX to SUN maintains high quality with CocoConvert's optimised encoder settings.
CocoConvert processes your FAX file on secure servers in Germany — upload, convert, download. Your files are encrypted via TLS and automatically deleted within 24 hours. No account needed, no software to install, and it works on any device with a browser.
This conversion is ideal when you When you need a SUN file.
The conversion engine behind CocoConvert uses FFmpeg, Sharp, and qpdf — the same open-source libraries trusted by Netflix, YouTube, and enterprise platforms. Pro users can batch convert up to 100 files at once.
How to Convert FAX to SUN
- 1
Add your FAX file
Drag and drop your .fax file into the converter, or tap "Browse" to pick it from your device. Multiple files are supported for batch processing.
- 2
Pick SUN output
Select .sun as the target format. CocoConvert automatically applies the best quality settings for this conversion.
- 3
Start conversion
Hit the Convert button. The image engine processes your file server-side — no CPU drain on your device.
- 4
Save your file
Once done, download your .sun file. For batch jobs, download all at once as a zip.
What Happens When You Convert FAX to SUN
Your FAX file is decoded and re-encoded as SUN.
Your FAX file is uploaded and validated
The file is decoded (parsed into its raw data)
The data is re-encoded in SUN format
The converted file is ready for download
Format Comparison
FAX
.fax file
| Extension | .fax |
| MIME Type | image/g3fax |
| Category | Image |
SUN
.sun file
| Extension | .sun |
| MIME Type | image/x-sun-raster |
| Category | Image |
Should You Convert FAX to SUN?
When to Convert
- ✓When you need a SUN file
Frequently Asked Questions
Why won't my FAX file open?
FAX files may not open if your device lacks the right codec or application. Converting to SUN — a more widely supported format — usually resolves this. SUN is a widely used file format.
Is it safe to convert FAX to SUN online?
Yes. CocoConvert encrypts your file via TLS, processes it on isolated servers in Germany, and permanently deletes it within 24 hours. Your files are never shared or analysed.
Will I lose quality converting FAX to SUN?
Converting FAX to SUN maintains high quality with CocoConvert's optimised encoder settings. CocoConvert uses high-quality encoder defaults to preserve as much fidelity as possible.
How large can my FAX file be?
Free users can convert files up to 250 MB each. Pro users get a 5 GB limit per file, and Business API users have custom limits.
Can I convert FAX to SUN on my phone?
Absolutely. CocoConvert works in any modern browser — iOS Safari, Android Chrome, and all desktop browsers. No app required.
Versions are pinned in our worker Dockerfile and re-built via CI on every change.