LetterAgent
Mail physical letters by just asking your AI assistant.
Home > Guides > Fax resolution settings
Fine resolution is the right default for most faxes: it reads clearly without dragging out the call. Use standard for plain typed pages to keep calls short, and superfine only for small print, detailed forms, or handwriting the recipient must read exactly. The receiving machine quietly steps down to whatever it can handle, so a setting it cannot support never breaks the fax.
| Setting | Scan density | Best for | Relative call time |
|---|---|---|---|
| Standard | 203 x 98 dpi | Plain typed text, drafts, long documents | Shortest |
| Fine | 203 x 196 dpi | Most faxes: forms, letters, normal print | About twice standard |
| Superfine | 203 x 391 dpi | Small print, dense tables, fine detail | About four times standard |
| Ultrafine / Photo | Up to 406 x 391 dpi | Photos, grayscale images (rarely useful) | Longest; both ends must support it |
The 203 dpi across the page is fixed by the fax standard itself: every Group 3 fax machine scans 203 dots per inch horizontally, because that matches the old CCITT test charts and the thermal print heads built for them. Only the vertical density changes. That is why jumping from standard to fine doubles the data: the page is sliced twice as finely top to bottom, and each slice costs line time.
Ultrafine is the odd one. It is not part of the original fax spec the way fine and superfine are; it is a manufacturer extension, and both machines must support it or the setting does nothing. A photo sent at ultrafine still comes out as black-and-white dither, which is why experienced users skip it for images and use it for tiny print instead.
Nothing dramatic. During the opening handshake, the two machines compare capabilities and settle on the highest resolution both support. If you pick superfine and the receiver tops out at fine, the fax goes through at fine and nobody sees an error. This also means there is no penalty for setting fine and forgetting it: it is supported by effectively every machine sold in the last thirty years.
Less than you would think. When you send a fax through an online service or through LetterAgent, your pages are transmitted digitally to the fax provider and only converted to fax protocol for the last hop to the recipient's machine. The quality ceiling is the recipient's machine and the phone line, not your upload. You can still control quality at the source: send a clean, high-contrast PDF at real size, and avoid faxing a photo of a document taken in bad light.
LetterAgent's fax feature works this way. You describe the fax to your AI assistant, approve the exact quoted price, and it is sent to US and Canadian fax numbers. Fax is currently available in testing, so send times are not guaranteed, and there is no inbound fax.
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