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Message Limitations and Restrictions

Size Limitations

The total size of any message is 35 MB excluding MIME encoding overhead. This effectively limits attachments to just under 34.9 MB in order to accommodate the message body, as well. This limit is applied for sending and receiving to both internal and external recipients.

Recipient Limitations

The maximum number of recipients in the To: field of a message is limited to 500. The maximum number of recipients per message when using distribution groups is limited to 5,000. If your organization is larger than this, the recipient limits for internal distribution groups can be raised on a per-user basis.

Blocked File Types

The following file extensions are blocked.

ade adp asx bas bat bin chm cmd com cpl crt exe hiv hlp hta inf ins isp
js jse jtd lnk msc msi msp mst ocx oft ovl pcd pif pl plx reg scr sct
sh shb shs sys url vb vbe vbs vss vst vxd wsc wsf wsh

As part of our multi-layer anti-virus and anti-spam protection, you may receive one or more different messages depending on which layer blocks the attachment. The block list is identical between layers.

Held Attachments

Some file types, while not necessarily dangerous, can still pose some degree of danger to an end user or agency if they are maliciously crafted. Most commonly, these are archive and compression file types such as those created by programs like WinZIP (.zip and .zipx), WinRAR (.rar), and StuffIt (.sit). As such, additional protections are in place for these file types.

Please note that Microsoft Office documents are also archived and compressed files with extensions such as .docx, .xlsx, and .pptx. The restrictions listed below will also apply to these documents.

Archive restrictions include:

  • An archive file containing more than 20 levels of archive depth
  • The file contains more than 256 entries or files
  • Total maximum unpacked size (all files) is greater than 50 MB

If any of these rules are violated, Proofpoint will block your message.