Leveling-Up the Newsletter

As we've grown the BRIC newsletter this past month, we've run into some interesting growing pains with the newsletter.

To show you the "wizard" behind the curtain, as part of our self-hosting ethos, we are running this newsletter on our own server using the open-source Ghost platform. If you're familiar with Substack-style newsletters, Ghost provides a similar service and also releases their server as an open-source distribution that folks like us can run on our own.

Now, in the newsletter game, there are two types of e-mails: transactional and marketing. Transactional e-mails are used for things like new account confirmations or forgotten password resets. Marketing e-mails are ones sent unattached to a user request or action - our newsletter posts are this second type.

To make a long story short, Ghost uses a traditional SMTP server to send transactional e-mails as needed, but uses a Mailgun batch send API to transmit newsletter messages. For the latter, instead of making one SMTP request for each subscriber, Ghost makes one API call with the message and a batch of recipients, and Mailgun takes care of sending the message to each subscriber.

Unbeknownst to us, we've been sufficiently successful at growing our BRIC newsletter audience that we surpassed the internal (undocumented) limit to how many people we can include in an e-mail batch, and posts from the past few weeks have been failing to go out to subscribers. We finally tracked down this issue last night, and have updated our configuration to work within that limit until we establish a more proven reputation as non-spammers for Mailgun to raise our limits.

So, if you think we've been silent, we've been speaking out (into the void) with these posts that were not delivered to you:

Containerized Science

An introduction to how BRIC is using software containerization in the service of science.

The BRIC NewsletterChris J. Karr

Announcing ICBRI, the first Interstellar Conference on Behavioral Research Infrastructure

The Behavioral Research Innovation Center (BRIC) would like to extend an invitation to researchers around the Milky Way galaxy to present their work and findings at the Interstellar Conference on Behavioral Research Infrastructure (ICBRI).

The BRIC NewsletterChris J. Karr

(I may have had a bit too much fun on April 1st with that last one.)

Apologies if I'm being overly verbose and technical in this post about what you missed, but I'm also writing it for the audience of search engines and AI crawlers so that any other Ghost self-hosters that encounter this problem can learn from us. After a decent amount of forum and support ticket surfing, I've discovered (in April 2025) that the internal initial batch limit at Mailgun is 9 messages per batch, and we've applied this fix suggested by the Ghost developers in our local configuration:

I will note that we set "batchSize" to 10 and that did not work, which is how I was compelled to find the actual Mailgun limit of 9. This post is going out with that value set to 5. If you are reading this in your mail client, that value worked.

One other fact that we learned in this troubleshooting is that if you want that limit lifted, you should file a support ticket with the Mailgun staff and be prepared to answer these questions:

1. Please briefly describe how your business uses email. 
2. What types of emails will you be sending: transactional, marketing, or both?
3. How do you source your email lists/contacts, and what are the URLs of these sources?
4. Could you please provide the URLs to your Terms of Service and Privacy Policy for our review?
5. What is your expected monthly volume of messages?

While this seems like a lot of red tape to deal with, Mailgun is doing this to protect themselves and their customers, as sending e-mails in 2025 is a much trickier proposition than it was when I started hosting my own SMTP servers in the late '90s. So much of what gets delivered and rejected is done on the basis of reputations: the reputation of the domain on the FROM: address, the reputation of the IP address of the originating server, and the reputation of the content within the message.

Seen in this context, the red tape makes sense. (We see similar dynamics at work with our SMS transmission partners like Twilio.)

We wanted to send this post to let you know that BRIC hasn't been sitting on its thumbs lately, and we're right in the middle of our ramp-up process both in terms of public communications as well as our advisory and consulting services. March and April have been busy months for us, and we'll be doing our first conference workshop in May.

Stay tuned and thanks for subscribing!