We were facing this issue as well. It was an internal issue from mailgun. The IP address of their SMTP was disabled so the mails were not able to be sent.
The customer support resolved the issue after 6 days of being unable to send any mails from that domain.
We were facing this issue as well. It was an internal issue from mailgun. The IP address of their SMTP was disabled so the mails were not able to be sent.
The customer support resolved the issue after 6 days of being unable to send any mails from that domain.