My test email failed - how can I find the source of this problem?
Using Jamroom
Probably the issue is the changes at mailgun. About 3 months ago you probably started getting invoices from them each month for maybe $0.80 for emails.
they removed their free tier which included 10,000 emails for free and email aliases.
I can see your server is still setup with an mailgun key:
https://www.jamroom.net/researchcooperative/hosting/server_config/37
This means you're running on your own mailgun account. We've just built a system to get around this: What we've built is a way for you to run off of our mailgun account. We pay the $30 per month so that routing can be enabled.
If you'd like to be moved over to this new system we can delete your mailgun key from your account and you can use ours if you like.
ADVANTAGES:
* no fixed monthly fee
DISADVANTAGES:
* per 1000 emails are slightly higher than if you had your own mailgun account
-------
Email Delivery
Jamroom Hosting uses Mailgun for all email delivery.
The first 1,000 emails sent or received each month are free - additional email is charged at a rate of $1 per thousand sent or received.
You can also use your own Mailgun plan if you wish - contact support and we can set you up.
--------
https://www.jamroom.net/hosting
You WILL need to re-setup each of the email aliases again after I remove the mailgun api key though, so make sure you keep a record of the aliases you have.