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Quick answer: Most failed faxes come down to the number, the line or the machine at the other end. Check the number has a 1 and the area code (or 011 and the country code), make sure it’s a fax line rather than someone’s phone, and if it’s busy, try again later. A “communication error” on a machine’s report points at the phone line: resend, or try a different line. A fax that arrives blurry needs a cleaner scan or a finer resolution.
A fax either fails to connect, connects and drops, or goes through and arrives in a state nobody can read. Each has its own short list of causes, so start with what you actually saw. This guide goes through each one, with the error messages machines print and what to do about them.
It won’t send at all
The number is the usual culprit. Dial a US fax number with the 1 and the area code, since some lines need both even for a local call; an international one needs 011 and the country code, without the leading 0 some countries print. Our guide to dialing a fax number has the rules, and fax number formats shows what a correct one looks like.
If a person or a voicemail greeting answers when you call the number, it’s a voice line, and no fax will ever get through to it. Ask for the fax number instead.
Then the other end. A fax machine that’s switched off, out of paper or full can’t take your fax. Brother’s machines, for example, show “Out of Memory” when their memory fills up. A quick call to the recipient settles it.
On a machine of your own, check your side too. Brother says its machines report “No Response/Busy” when there’s no dial tone, and when the phone cord is in the EXT socket instead of LINE. If your phone company has recently moved your line off copper, that can be the cause as well; the section on internet phone lines below covers it.
On an office phone system, you may need a code, such as 9, to reach an outside line. Most machines let you save it in their settings: Epson, for one, has you register the access code on the machine.
Busy, again and again
Brother’s explanation of its “No Response/Busy” message covers both cases: the number was engaged, or nothing answered. Its advice is to ask the recipient whether their fax machine or line has a problem and, if not, to send at a different time of day.
Reading the error on the report
Machines print or display a short message when a fax fails. The wording differs by maker, and many add a numeric code; HP lists its codes on its support site. Brother’s messages are typical of what you’ll see:
Common fax error messages and what to do
Messages and causes from Brother’s manual for the MFC-3360C, checked on 18 October 2026. Other makers word them differently.
| Message | What it means | What to do |
|---|---|---|
| Comm. Error | Poor phone line quality interrupted the fax | Send it again, or connect the machine to another line. If it keeps happening, ask your phone company to check the line |
| No Response/Busy | The number was busy or didn’t answer | Check the number and try again later |
| Disconnected | The other party or their machine ended the call | Send it again |
| Out of Memory | Your machine’s memory is full | Print or clear the faxes stored in memory, then retry |
On an internet (VoIP) phone line
If your machine plugs into a box or router from your phone or cable company rather than a wall socket, the line runs over the internet, and fax tones don’t always survive the trip: the call connects, then the fax fails partway through. Slowing the machine down usually helps. Brother’s “Basic (for VoIP)” setting drops the speed to 9,600 bps and turns off error correction mode (ECM), and Xfinity asks fax users to turn off ECM and call waiting. Epson also suggests turning ECM off if the line has static.
Our guide to landline shutdowns and fax machines lists the rest of the settings to try, with what each phone company says about faxing.
It says sent, but they didn’t get it
A confirmation page shows that your fax reached the number you dialed, so look at the number printed on it first. A single wrong digit sends a perfectly good fax to the wrong machine.
If the number is right, the fax arrived somewhere at their end. In an office it may be sitting on a shared machine, and if they receive faxes by email, it may be in a spam or quarantine folder. Ask them to check before you send it again, so the second copy doesn’t add to the confusion.
It arrived blurry or unreadable
A fax is black and white only, at a lower resolution than a screen or a printer. Anything faint, gray or colored has to be turned into solid black or white on the way, and pale ink, pencil and phone photos with shadows come off worst.
Most machines let you choose the resolution before sending. Brother’s options are typical: Standard for most typed documents, Fine for small print, Super Fine for small print or artwork, and Photo for photographs and shades of gray. The finer the setting, the slower the fax. For anything with small text, use Fine, which sends at 204 by 196 dots per inch. Clean the scanner glass as well, which Epson suggests for poor fax quality: a mark on the glass is copied onto every page you send.
When you send from a phone or computer, the service converts your file for you, usually with one cut-off for the whole page. Our fax optimizer converts a PDF to fax-ready black and white in your browser first, so you can see what the other end will get before you send it.
When you send from the app
An online fax service takes your own phone line out of the picture, which removes one whole set of causes. It can’t fix a busy, switched-off or wrongly numbered machine at the other end. In Municorn Fax, a fax that doesn’t go through shows as failed in the app, so you know to check the number and send it again, and the app has live support if it keeps failing. You can test a number first with the free single-page fax; our guide to sending a test fax explains how.
Frequently Asked Questions
Can I send a fax to an ordinary phone number?
Only if a fax machine or fax service answers it. If a person or voicemail answers, the fax will fail every time.
Why did my fax arrive blank?
On a machine, the pages most likely went into the feeder the wrong side up, so it scanned the blank backs. Check the little diagram on the feeder and send again.
How many times should I try before giving up?
Two or three attempts at different times is usually enough to rule out a busy line. After that, call the recipient to confirm the number and that their machine is on.
Sources
- Brother, “Why does the message No Response/Busy appear on my Transmission Verification Report?” (FAX-2840): busy or no answer, the LINE and EXT sockets, no dial tone, try another time. Checked 18 October 2026.
- Brother, MFC-3360C user’s guide, error messages: Comm. Error, No Response/Busy, Disconnected, Out of Memory. Checked 18 October 2026.
- Brother, “Change the quality of the faxes I send (Fax Resolution)” (MFC-J6720DW): Standard, Fine, S.Fine and Photo. Checked 18 October 2026.
- HP, fax error codes and messages for HP printers and fax machines. Checked 18 October 2026.
- Brother, “Telephone Line Interference/VoIP” (MFC-J1010DW, MFC-J1012DW, MFC-J1170DW): the Basic (for VoIP) setting, 9,600 bps with ECM off. Checked 18 October 2026.
- Xfinity, “Troubleshooting your Xfinity Voice and fax machines” (last modified 31 August 2026): turn off ECM and call waiting. Checked 18 October 2026.
- Epson, “Cannot Send or Receive Faxes” (ET-15000): ECM off on a line with static; registering an outside-line access code. Checked 18 October 2026.
- Epson, “Fax Quality is Poor” (ET-15000): clean the scanner glass. Checked 18 October 2026.
