The promise of cryptocurrencies, and blockchain technology in general, is decentralization. Proponents say that if power is spread out to many different people and groups, then no single entity can impose its agenda on the whole network. In practice, however, cryptocurrency communities rely on many centralized tools.

For example, much of the discussion within cryptocurrency communities takes place on Twitter and Reddit. Using popular services like these is good for accessibility, but occasionally relying on an mainstream entity backfires on the cryptocurrency proponents.

Last week MailChimp, an email newsletter platform, decided to shut down accounts that promote cryptocurrencies and ICOs. But not completely. In response to complaints from the cryptocurrency community, MailChimp tweeted, "Cryptocurrency-related information isn't necessarily prohibited. It can be sent as long as the sender isn't involved in the production, sale, exchange, storage, or marketing of cryptocurrencies."

Technology analyst Ben Thompson suggested that the decision was motivated by deliverability concerns: MailChimp's success depends on its emails not being kept out of people's inboxes by spam filters. It sounds like he was right. MailChimp wrote in an email to Inc. that "the promotion and exchange of cryptocurrencies is too frequently associated with scams, fraud, phishing, and potentially misleading business practices at this time."

"We made this decision to update our Acceptable Use Policy in order to protect the millions of businesses that use MailChimp for their marketing," the company said. The policy also prohibits other types of businesses that are considered spam-prone and high-risk, from pharmaceuticals to gambling to affiliate marketing.

However, when it comes to cryptocurrencies, there appear to be gaps between policy and implementation. MailChimp indicated that sharing information about cryptocurrencies, as a journalist or news outlet might do, was still allowed. In practice, several newsletters have been hit by the policy change.

.@MailChimp I've spent thousands of dollars with you and sent hundreds of subscriber emails on crypto over the past five years.



I'm restarting my Daily Bit Monday. I don't shill ICOs. Don't fuck with me. pic.twitter.com/XHdWBUQGPF -- Ryan Selkis (@twobitidiot) March 30, 2018

This is the second instance I hear of @mailchimp shutting down accounts related to crypto-currencies. Not ones advertising ICOs, or even exchanges. Just news, books, event announcements. https://t.co/R424TfN50W -- Andreas M. Antonopoulos (@aantonop) March 29, 2018

Hola @mailchimp we've never violated the acceptable terms. We are NOT an ICO, we are a community of learners. Please unflag us. I'm happy to provide proof of 501c3 status or non-ICO-iness. https://t.co/VdVJJsYBJ6 -- Jinglan Wang (@jinglanW) April 3, 2018

Evan Van Ness, who runs Week in Ethereum, received a warning that his account would shut down within a month. In response to an inquiry about why Week in Ethereum was being kicked off the service, a company spokesperson responded, "MailChimp is looking into this particular account, but if an account holder believes there's been a mistake they're encouraged to reach out to legal@mailchimp.com with the details, and MailChimp's Legal team will take a closer look."

Van Ness didn't find that satisfactory, and plans to migrate to a different email newsletter service. "I think it speaks to their corporate culture that they want ME to do (a small amount of) work to beg for the privilege of continuing to pay them $1,000 a year to send emails," he told Inc.

Lawyer Nelson Rosario is in the process of building out a site called Law of Cryptocurrency. He also found out that his newsletter account would be shut down. "They told me to reach out to their legal team, which I did," Rosario said, "and I politely explained I didn't understand how my blog discussing court cases that mention Bitcoin had anything to do with their new Acceptable Use Policy, and yet here we are."

TFW it's day Four and no word from MailChimp legal about my, and others, blocked #Blockchain #cryptocurrency newsletter cc @pamelawjd pic.twitter.com/7vIcXo1EwT -- Nelson M. Rosario (@NelsonMRosario) April 3, 2018

Banning cryptocurrency discussion -- of some kinds -- is a bit of an anomaly for MailChimp. A spokesperson told Inc. that "MailChimp hasn't added a category to its [content policy] in several years."

Why is any of this important? From one perspective, it isn't: This is just another company adjusting its terms of service because it thinks a certain type of customer is a liability to the health of its business. Even a small dip in overall email deliverability could be devastating for other MailChimp customers, who depend on the marketing channel for revenue.

On the other hand, MailChimp's decision validates the whole decentralization value proposition that drives cryptocurrencies. Sure, there are other email newsletter platforms. Upstart Substack, which is sort of like Patreon for email newsletters, reached out to at least one unhappy former MailChimp customer.

But the principle remains that whatever you build on a centralized platform -- say, custom email templates or automation flows -- can be yanked out from under you at the whim of the controlling entity. The platform may say one thing while doing another, and you'll be stuck sending inquiries into the void. The level of accountability depends on the entity's whims.