Why is my fax not going through?

The most common reasons are a wrong fax number, a busy recipient line, a VoIP phone line that corrupts fax tones, or interfering devices (voicemail, call waiting) on the same line. Check the number first, then try the fixes in our [troubleshooting guide](/blog/fax-not-going-through/).

How do I know if my fax went through?

Your fax machine should print a transmission verification report (also called a confirmation page) after each send. A "RESULT: OK" means it was delivered. If you see "NG" or "ERROR," the fax failed. Online fax services like [mFax](https://mfax.to) send a delivery receipt by email or push notification.

How many times should I retry a failed fax?

Try 3-4 times at 5-minute intervals. If it still fails after 4 attempts, the problem is likely not a busy line — check the number, your phone line, and your machine settings before trying again.

Can you fax over VoIP?

Technically yes, but VoIP compresses audio in ways that distort fax tones, causing 5-20% failure rates. You can improve reliability by using the G.711 codec and T.38 protocol, but cloud fax services like [mFax](https://mfax.to) are far more reliable. See our full [VoIP fax guide](/blog/voip-fax-problems/).

What does 'communication error' mean on my fax machine?

A communication error means the sending and receiving fax machines lost their connection during transmission. Common causes include poor phone line quality, VoIP interference, or the remote machine hanging up. Lower your baud rate to 9600 and try again.

Fax Not Going Through? 8 Fixes That Actually Work

Your fax won't go through and you need it delivered now. Here are the 8 most common reasons faxes fail — wrong number, busy line, VoIP issues, and more — with step-by-step fixes for each one.

Frequently Asked Questions

Why is my fax not going through?: The most common reasons are a wrong fax number, a busy recipient line, a VoIP phone line that corrupts fax tones, or interfering devices (voicemail, call waiting) on the same line. Check the number first, then try the fixes in our [troubleshooting guide](/blog/fax-not-going-through/).
How do I know if my fax went through?: Your fax machine should print a transmission verification report (also called a confirmation page) after each send. A "RESULT: OK" means it was delivered. If you see "NG" or "ERROR," the fax failed. Online fax services like [mFax](https://mfax.to) send a delivery receipt by email or push notification.
How many times should I retry a failed fax?: Try 3-4 times at 5-minute intervals. If it still fails after 4 attempts, the problem is likely not a busy line — check the number, your phone line, and your machine settings before trying again.
Can you fax over VoIP?: Technically yes, but VoIP compresses audio in ways that distort fax tones, causing 5-20% failure rates. You can improve reliability by using the G.711 codec and T.38 protocol, but cloud fax services like [mFax](https://mfax.to) are far more reliable. See our full [VoIP fax guide](/blog/voip-fax-problems/).
What does 'communication error' mean on my fax machine?: A communication error means the sending and receiving fax machines lost their connection during transmission. Common causes include poor phone line quality, VoIP interference, or the remote machine hanging up. Lower your baud rate to 9600 and try again.