My Heroku app sends e-mails to an external SMTP server at port 25 rather than using a Heroku add-on. It seems that the app is intermittently having difficulty in sending e-mails.
You will likely see TCP connection errors in your logs. If you are using Rails ActionMailer you will see a slightly cryptic
Net::OpenTimeout·execution expired error in your logs and emails will not be sent.
Our infrastructure provider applies a throttle on egress network connections to port 25 by default.
To work around this, please:
- Use an alternative port to send e-mails. For example, Mandrill also supports ports 587 and 2525; or
- Contact Heroku Support with the name of the Private Space or the app to have the throttle removed for the Private Space
This throttle cannot be removed for Common Runtime apps.