Tax client file transfers

What is an online service that you use to have tax clients transfer data to you online? Drop box?

Encyro.com . Straightforward, secure, inexpensive, no whiz-bang gizmo "features" of dubious value.

Encyro

I use securefirmportal.com, part of the web services I get from CPASiteSolutions.com. There's a way to send files without an account, but I set up accounts for all of my clients, and the only way I provide PDF copies of returns is through the portal.

A few clients will send links from their own One Driver, Drop Box, etc. or just send through plain email, but our portal is the only thing we encourage.

I have a few paths to receive secure files.
I use SafeSend to deliver my tax returns. That platform comes with SafeSend Exchange, the link for which I put in my email signature. There is no additional cost to that, file size is practically unlimited, and anyone can use it. Great for one-off files or new clients.
I also use SafeSend for their organizers, which has a secure link for document upload in that process.
Lastly, my practice management software provides a portal for each client through which they can upload files directly to the doc mgmt system there.