File attachment limits are a bit tricky to describe: you have to set up your gateway with a specific limit and you also have to ensure that your ISP doesn't have other limits they impose that will prevent large attachments from being sent. Overall domain limits are set by the DataMotion support staff and not by the mail administrator. DataMotion has a separate file transfer product that can be used to send up to 2GB files.
Speaking of limits, DataMotion doesn't have any limits on the size of the user's inbox. However, it does place a limit of up to 500MB worth of messages that can be sent in a user's Track Sent Folder. If this limit is reached, the user will no longer have the ability to send new messages until space has been freed up within their account.
There are numerous features that are part of the DataMotion ecosystem: one of the more useful is its notifications feature, where you can see exactly when your recipient opened the message and the attachment. You can also set expiration dates for your messages, retract those that haven't yet been read, or resend another notification message via the Web app. Once a message expires, the only thing that remains is its metadata.
DataMotion offers a very robust set of APIs for developers to incorporate their programs with secure email features, along with a sandboxed cloud environment that can be used to test and track messages as they transit the Internet.
Subject lines aren't encrypted. Regarding the Silk Road scenario, while DataMotion couldn't completely protect against that situation, it can be setup so that no decrypted messages are ever stored locally.
DataMotion has a rather complex pricing sheet. You purchase the number of mailboxes (our sample 50 user set was $4,795 per year), then add on the Windows gateway for another $2,599 (which includes support), and if you want the large file transfer option that is another $72 per user per year. Free trials are also available.
Voltage has been in the encrypted email business for more than a decade, and recently was purchased by HP and rebranded. The technology is an email gateway, software that sits on either a Linux or Windows server or in the cloud and inserts the encryption process between mail client and server. There are numerous add-on modules that come as part of this ecosystem, including:
An option to send large attachments, including set expiration dates.
The Secure File desktop encryption client, which can be used to send files to a user directly, either from the desktop or directly from within Office apps.
Mobile clients for iOS, Android and BlackBerry. Voltage has separate clients that are very attractively designed and work very seamlessly with their ecosystem. Users can view attachments securely, too.
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