Hello Bryan,
I responded to you by email earlier with the below response. If you're still experiencing an issue please respond back to that email.
We haven't changed anything on our end and there have not been any reported issues regarding emails being sent from Method. The error message you're receiving states that your mail server was unable to relay the email(s). I would recommend you contact your email provider to figure out what happened. The most likely cause is that they only allow a certain amount of relay messages per month/day, which I've seen happen to some clients. This is nothing that Method has control over as this is something which would be set by the email hosting provider.
When you get in touch with them, ask if the limit can be increased or if there is another server which you can use to send open relay messages, then just change the server info under the Default Email Preferences section in Method.
- Ashur