Attachment and e-fax scanning delivery timing
Paubox automatically scans all email attachments and e-faxes to protect your organization from viruses and enforce data loss prevention (DLP) policies. While security scanning typically completes in a matter of seconds, downstream delivery factors and file complexity can occasionally impact processing time.
How attachment and e-fax scanning works
When an email or e-fax contains a scannable file—such as a PDF, Office document, spreadsheet, CSV, text file, or archive—Paubox inspects the content before releasing it for delivery. For image-heavy documents like e-faxes, the scanner performs text and optical character recognition (OCR) extraction.
Scanning standard documents usually takes only a few seconds. Larger or image-dense files require more processing time, and a sudden surge of heavy attachments can cause a short queue where messages wait briefly behind one another.
If an attachment violates a security or DLP rule, Paubox blocks or quarantines the message. Messages experiencing delivery delays passed all security checks and were not flagged as threats.
Primary causes of multi-hour delivery delays
A genuine multi-hour delay is rarely caused by the scanner itself. Instead, multi-hour delays almost always occur during the delivery phase after scanning has finished.
The primary reasons for extended delivery times include:
- Receiver-side throttling: The receiving mail server temporarily defers incoming messages, prompting Paubox to retry delivery on an automated backoff schedule that spaces attempts over several hours
- Queue backlogs: Spikes in mail volume create temporary processing queues where messages wait for downstream resources
- Scanner retries: Malformed or corrupt attachments trigger internal scanner retry loops before completing evaluation
Because receiving mail servers routinely throttle large transmissions, messages containing sizable attachments or multi-page e-faxes are the most susceptible to receiver-side deferrals.
Attachment size limits and best practices
Paubox supports a maximum total attachment size of 50 MB per message. Files approaching this ceiling take longer to extract and are significantly more likely to be deferred by the receiving server.
To minimize delivery delays:
- Reduce image resolution or split large e-fax transmissions into smaller files
- Flatten interactive PDF forms before attaching them
- Avoid wrapping attachments in multi-layered .zip or .7z archives