I just spent a few hours debugging my rails app on Heroku to understand why the hell I did not systematically receive the monitoring emails that my app was sending …
My app was actually rendering the email template.
Wether the mail came through actually depended on the mail content !
It seems there was a spam filter somewhere between the sender and the receiver that was blocking some emails, without warning me in any way. I was sending the email to a custom domain email from ‘OVH’ and then forwarding emails to my gmail account, it was handy to apply automatic labels.
Here is the #1 rule : always send your monitoring emails directly to the final recipient ! There will be less risk that some messages get lost.
I changed the recipient to my gmail address, updated my label filter, and everything is back to normal (a lot of time lost for nothing).