> ## Documentation Index > Fetch the complete documentation index at: https://payperfax.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Fax Marked as Sent But Not Received > Understanding why successful transmission doesn't always mean immediate receipt Your fax shows as "sent successfully" but the recipient says they didn't receive it. This page explains why this happens and what to do. ## Understanding "successful" transmission **"Successful" means the receiving fax machine confirmed receipt** - not that the recipient has the fax in hand. When PayPerFax reports success, it means: The destination fax line picked up the call Both machines agreed on transmission parameters All pages were sent over the fax line The receiving machine sent a confirmation signal (CSID) **This does NOT guarantee**: * The recipient checked their fax machine * The fax printed correctly * The fax was routed to the right person * The recipient received/read the fax ## Common reasons recipients "didn't get it" **Most common reason** The fax printed successfully but: * Nobody checked the fax machine yet * Fax is buried under other received faxes * Fax tray is full and fax fell behind/under machine * After-hours delivery and not yet noticed **What to do**: Ask recipient to physically check the fax machine and tray In large organizations with shared fax machines: * Fax delivered but routed to wrong person/department * Sitting in general mailroom * Cover page didn't specify recipient clearly enough * Internal mail system delay **What to do**: Ask recipient to check with mail room or other departments The fax transmitted but printed poorly or blank due to: * Out of toner/ink * Paper jam during printing * Receiving machine print head issues * Fax machine saving to memory due to paper out **What to do**: Ask recipient to check their fax machine display and print queue * Fax sent late at night (recipient's time) * Next business day hasn't started yet * Weekend delivery not checked yet **What to do**: Wait until business hours in recipient's time zone If destination is a fax-to-email service: * Email might be in spam/junk * Email server delays * Incorrect email configuration * Service issues on their end **What to do**: Ask recipient to check spam folder and fax-to-email service status ## What the confirmation tells you Your confirmation email includes: Exact date and time the fax was sent Verify with recipient's time zone Called Subscriber Identification from receiving machine Confirms the specific machine that received it Number of pages transmitted Ask recipient if they received this many pages Exact image of what was sent Show this to recipient for comparison ## Steps to resolve Check your confirmation email: * Shows "Success" or "Delivered"? * Has CSID (receiving machine identifier)? * Includes PDF attachment? If yes to all, transmission definitely completed. Call or email the recipient: * Ask them to physically check the fax machine * Provide the date/time of transmission * Give them the CSID if they have multiple fax lines * Ask about their check their spam (if fax-to-email) Send the PDF from your confirmation email to recipient via email as an alternative. This proves: * What was sent * When it was sent * That transmission completed If urgent, wait a few hours and ask recipient to check again: * In-office mail distribution takes time * Shared fax machines may have backlogs * After-hours deliveries need business hours If truly lost: * Resend the fax * Use cover page with clear routing instructions * Include attention to specific person/department * Consider adding "RESEND" in subject See [How to Resend](/troubleshooting/resending-faxes) ## Technical explanation Fax transmission works like postal mail: **PayPerFax's role** = Post office * We deliver to the destination mailbox (fax machine) * We confirm it was accepted by the mailbox * We provide proof of delivery **After delivery**: * Recipient must check their mailbox (fax tray) * Internal routing is their responsibility * Physical pickup is their responsibility We can prove it was delivered to their fax machine, but cannot control what happens after that. The **Called Subscriber Identification (CSID)** in your confirmation is key evidence. This identifier comes from the receiving fax machine itself after successfully accepting all pages. **It's like a delivery signature** - proves the destination fax machine received and acknowledged your fax. If you have a CSID in your confirmation, transmission definitely completed to that specific fax machine. ## What PayPerFax guarantees ✅ Transmission to receiving fax machine ✅ Handshake and receipt confirmation ✅ All pages sent successfully ✅ CSID received from destination ✅ PDF proof of what was sent ❌ Recipient checking their fax machine ❌ Print quality at destination ❌ Internal routing at large organizations ❌ Recipient's fax machine toner/paper ❌ Physical retrieval of printed fax ## When to contact support [Contact PayPerFax support](https://payperfax.com/contact-us/) if: * Your confirmation shows "Failed" but recipient claims they got it * No CSID in confirmation but status shows "Success" * Confirmation email looks suspicious or incomplete * Need help interpreting technical details **For "sent but not received" scenarios**: This is typically a recipient-side issue. Share your confirmation email/PDF with them to help locate the fax. ## Alternative delivery If the fax repeatedly shows as sent but recipient can't find it: Use the PDF attachment from your confirmation email: 1. Forward the email to recipient 2. Upload PDF to shared file service 3. Print PDF and mail it traditionally This bypasses their fax machine issues entirely. ## Related topics Understanding the fax process How to send again if needed Other troubleshooting topics Frequently asked questions