Weezo.net, its software you install & has literally thousands of uses for sharing, hosting your own site. Not entirely sure on its security/encryption but i find it useful in so many ways.Its windows only software but is based in php for the majority so i'm sure a coder could adapt for other os's. The only downside is its french speaking forum for help, even in these days of translation software its sometimes hard to follow along BUT dont let that put you off giving it a go its actually setup to work out of the box pretty simply from the off for 99% of configurations its only the odd one that falls foul of the odd quirks now & again.

I totally prefer www.copy.com you get 20GB of free storage and it has the ability to share files in a few different ways including e-mail, you can decide whether tho place security on a share or not, and of course you can remove the share links at any time. This alone makes it way more secure than any e-mail and the likely hood of the e-mail dropping the link would be virtually unheard of. As stated by another, there are many sites out there that offer these services, and as to the security of them ,,, well, for a great part that relies on your handling of your account password, to be a good password you cannot use any dictionary based words or names, they need to be at least 8 characters (preferably more) with a mixture of upper and lowercase letters, a number, and if allowed a special character (ie. !?#~ etc.). At any rate, if you want to keep it as simple for others that need to access the file, stay away from proprietary bullying, you do not want a service that requires you to install their client on the computer receiving the file, to do so negates the whole en-devour.

I personally use a Virtual Private Server that I already had with an installation of OwnCloud (http://owncloud.org) with file encryption enabled. It's secure, the software is free, it's *mine* and you can host it anywhere that php/mysql are supported. It's not difficult to set up for most geeks, and I'm sure there are places that sell OwnCloud hosting as well.

I don't quite undestand why you are asking for an "alternative to Dropbox" as by your own account you have been using email to transfer the files. Likewise, how secure does the system need to be? Email, after all, is not so secure...Yaara's article provides a pretty good list to begin with. BitTorrent Sync is a good solution, but may not be would be simple enough for your clients. Hightail.com (formerly yousendit.com) allows you to send files either directly from the desktop via an app. Finally, there are many file sharing sites with security features. My favourite is minus.com which is easy to use and allows you to set passwords to files or folders. Wikisend.com also looks very good, althoguh I haven't tried it myself.

The safest, simplest alternative to DropBox and other cloud storage is an external drive that you control.

We've written about some ways to make Dropbox safer, as well as security-minded alternatives.http://www.makeuseof.com/tag/create-your-own-secure-cloud-storage-with-seafile-2/http://www.makeuseof.com/tag/securing-dropbox-6-steps-to-take-for-safer-cloud-storage/http://www.makeuseof.com/tag/5-ways-to-securely-encrypt-your-files-in-the-cloud/BitTorrent Sync and SpiderOak are two options you may choose for security over Dropbox, but BT Sync is slightly more complex than Dropbox, so it might not be the best option for your situation.http://www.makeuseof.com/tag/from-pirate-darling-to-dropbox-alternative-bittorrent-sync-lets-you-keep-your-files-synchronized-across-machines/http://www.makeuseof.com/tag/spideroak-online-data-backup-sharing-solution-crossplatform/http://www.makeuseof.com/tag/secure-files-3-encrypted-dropbox-alternatives/