LetterAgent
Mail physical letters by just asking your AI assistant.
Sometimes, but it is unreliable. Fax tones were designed for the steady timing of the old analog phone network, and VoIP compresses, packetizes, and occasionally drops pieces of audio. A page can still get through on a clean connection, especially with the T.38 fax protocol, but on a jittery line the handshake fails and the fax drops.
Fax machines talk to each other with precisely timed audio tones: the handshake that opens the call, the negotiation of speed and resolution, and the page data itself all ride on tone timing measured in milliseconds. The analog phone network delivered those tones with rock-steady timing. VoIP does three things that break that steadiness. First, compression codecs throw away audio detail to save bandwidth, and the detail they throw away includes parts of the fax tones. Second, packets arrive with jitter, small timing variations that a human ear never notices but a fax modem reads as corrupted data. Third, lost packets create gaps, and a gap in the middle of a page block triggers a retransmission, which on a bad line cascades into a failed call. More bandwidth doesn't fix it; a gigabit fiber line with jittery routing faxes worse than a clean low-bandwidth one.
T.38 is a protocol built specifically for sending fax over IP networks, and it's the closest thing to a real fix. Instead of treating fax tones as audio, T.38 converts the fax data into IP packets at the gateway, carries them across the network as data, and converts them back to tones at the far end. When both your VoIP provider and the receiving side support T.38, faxing becomes dramatically more reliable. The catch is the "both sides" part: T.38 has to be supported end to end, and many consumer VoIP adapters and providers don't implement it, or implement it badly. If your provider's help pages don't mention T.38 or "fax support," assume you don't have it. Some providers offer a dedicated fax line or fax-to-email service as a separate product, which is their honest admission that fax over their voice lines is a gamble.
| Setting | What it does | Why it helps |
|---|---|---|
| Slower baud rate (9600) | Drops the modem speed | Slower tones survive compression and jitter better |
| ECM off | Disables error correction | Stops the retransmission spiral that kills calls on noisy lines |
| G.711 codec | Uses uncompressed audio | Preserves tone detail that compressed codecs discard |
| Wired connection | Eliminates Wi-Fi jitter | Steadier packet timing end to end |
These are damage control, not a cure. They raise your odds from poor to decent on a good day, and they do nothing on a bad network day. If you're troubleshooting a fax machine plugged into a VoIP adapter, check whether the adapter has a "fax mode" setting; many do, and it typically forces the G.711 codec and disables the echo cancellation that mangles fax tones.
If you've tried twice and the handshake keeps failing, stop. The line isn't going to improve, and each failed attempt costs you time. Online fax services transmit from commercial phone lines with proper fax signaling, so the VoIP problem disappears entirely: you upload the file, the service sends it from its own equipment. LetterAgent works this way: describe the document to your AI assistant, approve the exact quoted price, and the fax is sent to US and Canadian fax numbers. Fax is currently in testing, so check with your assistant about availability before you count on it for a deadline.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
Need help? Ask your assistant: it can check a job's status any time. If it ever can't handle something: hello@getletteragent.com