With Mandrill functionally going the way of the Dodo as far as Rock is concerned, The Core Team has added Mailgun integration for sending email. The Communications documentation available here has instructions on getting Mailgun set up and configured with Rock.
We migrated our Rock install to Mailgun and ran into a few things that needed to be tweaked. As these things aren't covered in the docs, I wanted to share them here.
After our first big mailing with Mailgun, we noticed a larger than expected number of failures. After some research, we found that Cox and AOL were bouncing emails because they could not resolve MX records for our Mailgun subdomain (mg.centralaz.com). So, I created a sumbdomain in our public DNS for 'mg.centralaz.com' and added the two MX records Mailgun lists in their docs for receiving mail. I didn't do this initially since I figured we were only sending through Mailgun. But, some services need these DNS records to resolve.
So, our public DNS now contains the following Mailgun-related entries:
A record: mg.centralaz.com
TXT record: mg.centralaz.com
TXT record: k1._domainkey.mg.centralaz.com
MX record in subdomain: mxa.mailgun.org
MX record in subdomain: mxb.mailgun.org
We also were having an issue with our internal users (people on our internal network) using links in the emails sent from Rock. Mailgun re-writes the URLs on links in emails so it can track clicks, etc. To make sure these re-written URLs worked, I added the 'mg' subdomain to my internal AD domain and added:
CNAME record: 'email' pointing to 'mailgun.org'
So, the FQDN is 'email.mg.centralaz.com' and it points to 'mailgun.org.'
I hope this information helps you. Like everyone, we are early in our Mailgun adoption/integration in Rock. If we run across any other gotchas, I will be sure to share them here.
If you have any tips or tricks, please share them in the comments.