You sent a PDF. The company mail server rejected it. The recipient's IT policy blocks the attachment. Or your own outgoing server stopped it.
What's actually going wrong
Corporate filters block PDFs for various reasons. Size policy. Enterprise mail servers often cap attachments at 10MB or less. Content scanning. PDFs with forms, scripts, or specific content patterns trigger blocks. Macro-like behaviour. Some PDFs contain JavaScript that filters treat as security risks. Sender reputation. New senders or domains flagged as suspicious.
The quick fix
Size: Compress PDF in Flint. Most files come well under typical corporate limits.
Content: Simplify the PDF. Convert to JPG and back to remove scripts and form fields — image-based PDFs rarely trigger content filters.
Channel: Use the company's approved file-sharing platform (SharePoint, OneDrive for Business, internal portals). These bypass email filters entirely.
If that didn't work
Contact IT. They can whitelist specific senders or files for legitimate exceptions. Persistent blocks often need policy-level resolution rather than technical workarounds.
For external senders trying to reach a corporate recipient, ask the recipient to add you to their safe-sender list, or use their approved external collaboration tool (often Box, SharePoint, or a vendor portal).
Prevent it next time
Use approved channels for corporate recipients. Keep PDFs simple — fewer features, fewer filter triggers. Build trusted-sender relationships with key recipients' IT.
FAQ
Why does my PDF trigger a corporate filter?
Size, content type (forms, scripts), or sender reputation. Filters are tuned to block malware vectors, and PDFs are common malware carriers, so suspicion is high.
Will compression help bypass filters?
Sometimes — if the block is size-based, yes. If content-based, no. Try compression first; escalate to alternative channels if blocks persist.
Can I make my PDF less suspicious?
Remove form fields, scripts, embedded files, and any active content. Convert to a flat image PDF if necessary. Filters generally pass simple PDFs.
What's the best channel for corporate recipients?
Whatever they specify. Most enterprises have an approved collaboration tool — using it ensures delivery and respects their security policies.
Corporate filters require working with IT, not around them. Compress and simplify in Flint, then use approved channels.