The term "paywalls" is commonly used to describe the commercial practice of requiring inbound traffic for a transaction (registration, payment) before granting access to content. However, more and more often, users and publishers alike are encountering elements of the digital ecosystem asking outbound traffic to pass certain standards or meet certain criteria, as well.

I've taken to calling these "pushwalls" -- barriers to getting your content or online business out to customers and users.

It's no longer safe to assume that users or digital publishers have an unfettered, straight path on the open Web to purveying content or even having their content seen or discovered. New elements -- the Great Firewall in China, geoblocking, ad blockers, spam filters, profanity filters -- create new impediments in digital publishing.

In scientific publishing, with tech-savvy users now the norm, ad blocking is particularly concerning for many publishers. Advertising is a way to diversify revenues and lower subscription rates or, for OA publishers, APCs. Whether those ads are in-house promotions -- calls for papers, announcements of meetings, appeals for membership -- or traditional commercial advertising, the percentage of users blocking these ads should be known. In one case I've seen, it's as high as 20%, which means that 1 in 5 users will not see these messages. That is a significant pushwall that can move commercial behavior away from advertising and back to charging users. In effect, users are blocking one commercial option in a way that will simply move publishers back to another commercial option -- asking users to pay directly. Yet this pushwall is growing in size.

The Great Firewall in China also poses barriers to scientific content, which can consist of materials and opinions the Firewall does not initially tolerate. Technology practices can also create barriers, as Google elements -- because of various ongoing and past dustups between Google and China -- often trigger a reaction within the Great Firewall, which blocks APIs and other elements from displaying.

Email continues to be the coin of the realm for driving awareness and the traffic pulse of journal sites, and spam filters have improved immensely in recent years, but some messages still get caught unexpectedly, and changes to email systems and practices have to be done carefully to ensure white-listing and compliance with best practices.

Social media pushwalls aren't as visible, but scientific content can trigger them inadvertently, especially if anatomical parts are described in headlines or included as images. Some systems have a Puritanical streak, and certain articles and headlines crash and burn against their pushwall.

Recognizing where delivery barriers exist, how to overcome or avoid them, and remaining adaptable to a slightly byzantine online publishing infrastructure is now a requirement for successful online business and publishing. It's not as simple as hitting "publish." There's a lot more to it these days.