Skip to main content

Set Options to Zip Mail and Attachments

PK Protect Attachments is an extension module to PK Protect for Windows that lets you automatically compress message attachments into a ZIP file when sending email messages or meeting requests using Microsoft Outlook.

You can also encrypt and sign message attachments, as well as the message itself (though not a meeting request), using current settings for encrypting and signing.

When you encrypt attachments, PK Protect zips the attachments a bit differently depending on whether you also encrypt the message.

Zip and Encrypt Attachments but Not the Message Body

When you send a message and zip attachments, PK Protect compresses and adds the attachments to a ZIP file and sends this in place of the original, uncompressed files. If you turn on Encrypt attachments (see the table of (17.8) Set Options to Zip Mail and Attachments#OutgoingOptions, below), PK Protect also encrypts the attachments. The ZIP file is given the name specified in the Default ZIP name option (see below) if it contains multiple files or if the Encrypt file names option is on. With a single file attachment, the ZIP file is ordinarily named after the attached file.

Zip and Encrypt the Message Body Too

With the Encrypt message body option checked, PK Protect encrypts the body of your email message in addition to file attachments. PK Protect first converts your message with its attachments into a single MIME-format .eml file and then encrypts and zips this file. The name of the .eml file, like the name of the containing ZIP file, is based on the subject of the message plus a timestamp: for example, My message subject 2015-10-05 14_19_27.EML.

If the subject is blank or contains any non-ASCII characters, the word PKMESSAGE is used instead. For example: PKMESSAGE 2015-10-05 14_19_27.EML.

Receiving and Opening an Encrypted Message

When your message is received and opened but is not yet decrypted, a message recipient sees only an announcement that the attached ZIP file contains a message encrypted by PK Protect. The announcement informs that PK Protect can be used to extract your message.

  • A recipient who does not have PK Protect can use ZIP Reader to decrypt and extract the .eml file that contains your real message and encrypted attachments. The .eml file can then be opened manually (for example, by double-clicking it in Windows Explorer) in an email program such as Outlook. Opening the .eml file decrypts and displays your real message and makes any attachments accessible.

  • For a message recipient who has Outlook and SecureZIP 11 or later, PK Protect automatically prompts for any necessary passphrase, decrypts and displays your real message in Outlook if the recipient has turned on the option Automatically decrypt messages when read (see the table of (17.8) Set Options to Zip Mail and Attachments#IncomingOptions below). Any attachments are also extracted and listed just as if neither message nor attachments had ever been zipped.
    If the Prompt before automatically decrypting option is checked, PK Protect asks first whether to decrypt.

  • Any message recipient who has PK Protect or SecureZIP 11 or later can also open an .eml message file manually (for example, by double-clicking it) either in PK Protect or after extracting it. Manually opening an .eml file in PK Protect displays its message, with any attachments, in the internal PK Protect MIME viewer, by default, or in whatever program is associated with .eml files on the user's system (for example, Outlook).

Note: The option to use the PKWARE MIME viewer with .eml files is a check box on the General page of Miscellaneous options. The MIME viewer displays the message and lists attachments in a conventional message window, but the viewer is not an email program: You cannot, for example, reply to a message directly from the MIME viewer. The viewer is provided because it may be more convenient than Outlook for recipients who do not already use that program. The first time it is run, Outlook presents several configuration dialogs before displaying the message in an .eml file.

An encrypted message is stored encrypted in Outlook: it must be decrypted each time it is read. Someone who opens an encrypted message but does not decrypt it sees only the announcement explaining how to view it.

Mail Options

You set options to control how mail attachments are handled on the General page of Mail options. Options to control which types of files are zipped and whether attachments totaling less than a certain size are zipped at all are presented on the Filter page.

To set general options for PK Protect Attachments:

  1. Select Options from the Application menu.
  2. Select the Mail category.
  3. On the General page, check boxes to select the options you want.

Outgoing Mail Options

You can set the outgoing mail options listed in the table below.


What It Does

Compress attachments

Turns on PK Protect Attachments: Causes PK Protect to compress attachments into a ZIP file and attach the ZIP file in place of the original attached files.

Prompt before processing

Causes PK Protect to ask first before zipping mail attachments. In the prompt dialog, you can specify a name for the ZIP file and set or unset options to encrypt attachments (or message body), digitally sign, include UNZIP instructions, and turn off future prompting.

Prompt before performing 'Always ZIP'

Causes PK Protect to ask you to confirm that you want to zip an attachment when both of the following are true:

  • The file type of the attachment is listed in the Always zip control (on the Filters page of Mail options)

  • Zipping is turned off or another option is set that would normally cause the attachment not to be zipped

Encrypt attachments

This setting controls whether PK Protect encrypts attached files when adding them to the ZIP file. By itself, the setting applies only to files that are not already ZIP archives. To encrypt (or re-encrypt) ZIP archives that you attach, set this option and also set Re-encrypt attachments (see below).

PK Protect encrypts attachments, using the current settings (for method, algorithm, and so on) on the ZIP page or OpenPGP page of Security options, even if Encrypt files is not checked on that page. If Encrypt attachments is unchecked, PK Protect does not encrypt attachments.

Encrypt message body and attachments

Converts your message along with any attachments into a single MIME-format .eml file, encrypts the .eml file, and places it in a ZIP file attachment. Message recipients see an announcement that the attached ZIP file contains an encrypted form of your message. The announcement explains how to extract and view your message.

If you receive such a message, PK Protect automatically decrypts and opens it in Outlook if you set the PK Protect incoming mail option (see below) Automatically decrypt messages when read.

Skip actionsSend your message and any attachments without compression or encryption.

Re-encrypt attachments

Enables you to change the encryption on existing ZIP archives that you attach to an email message. Use when you want to send or forward a ZIP archive that may not be encrypted for the people you want to send it to. This option must be set if you want PK Protect to encrypt existing archives. Set Encrypt attachments (see above) to enable this option.

See here for more information on re-encrypting attachments.

Auto-search for recipients

Automatically takes everyone named on the TO:, CC:, or BCC:lines of the outgoing email message and adds them to the recipient list for an encrypted attachment. Works only if PK Protect is set to encrypt files using a recipient list. Set Encrypt attachments (see above) to enable this option.

If PK Protect cannot find a certificate for every recipient, PK Protect gives you the following options:

  • Encrypt with passphrase for recipients without a certificate

  • Encrypt only for recipients for whom certificates were found

  • Do not encrypt the attachment

Note: When this option is checked and you send a message with a zipped attachment, a Microsoft Outlook warning dialog may open to display a message that a program is trying to access email addresses you have stored in Outlook. The dialog asks if you want to allow this.

It is normal for this dialog to appear if you are encrypting an attachment with a recipient list. In the dialog, check the box Allow access for 1 minute and click Yes to proceed. If you are encrypting for a large number of recipients, you may need to change 1 minute to a longer period in the dialog.

See here for information about the recipient list method of encrypting files.

See here for information about pointing PK Protect to a directory server to look for certificates for recipients.

Sign attachments

This setting controls whether PK Protect digitally signs attachments. If the box is checked, PK Protect signs attachments, using the current settings on the ZIP page or OpenPGP page of Security options, even if Sign files is not turned on in Security options. If Sign attachments is unchecked, PK Protect does not sign attachments.

Include extract instructions

Causes PK Protect to include with any zipped attachment a small, additional attachment with instructions on how to download the free ZIP Reader by PKWARE application to use to unzip ZIP files

Default ZIP name

PK Protect gives the same, generic name to all ZIP file attachments that contain multiple files. In this field, specify the generic name to use.

When you zip a single attached file, ordinarily the ZIP file is named after the attached file itself. For example, if the attached file is my_file.doc, PK Protect names the ZIP file (Exception: If the Security option to Encrypt file names is set, the generic name is always used, even if option Use original name for single attachments is set and the attachment contains a single file.)

Following the Default ZIP Name, you can also define an alternate three-character extension for ZIP archives. Some networks have security settings that prevent file attachments with the ZIP extension from being sent or received. Use this feature if this is an issue for you or your recipient.

Use original name for single attachments

This option affects zipped file attachments that contain a single file. The option tells PK Protect to name the file attachment after the file it contains (unless the Security option to Encrypt file names is set, in which case the generic, default ZIP name is used).

Uncheck the option to use the default ZIP name (see the option just above) for all zipped attachment files.

Keep options in sync with Outlook ribbon buttons

Check this box to ensure that if you change PK Protect options (encrypt or sign) in Outlook, this option will change in PK Protect Options as well. Note that if you check this box to synchronize the options, PK Protect may take longer to load.  

Incoming Mail Options

The table below lists options for working with email you receive that the sender encrypted using PK Protect with the (17.8) Set Options to Zip Mail and Attachments#EncryptMsgBody option set.


What It Does

Automatically decrypt messages when read

Automatically decrypts and displays email messages that the sender encrypted using PK Protect with the option Encrypt message body set. Decrypted messages are opened in Outlook.

Prompt before automatically decrypting

Asks whether to decrypt and display an email message that the sender encrypted using PK Protect with the option Encrypt message body set. The prompt displays when you open the message in Outlook. If you choose No, only the cover announcement that the message is encrypted by  PK Protect can be read.

JavaScript errors detected

Please note, these errors can depend on your browser setup.

If this problem persists, please contact our support.