The following information applies to the Mailgun integration with Mintsoft.
Forbidden IP Address
Errors (Unable to Send Despatch Email to: x Error:Unable to send Email. Exception: MailGun - Unable to Send Email, Status: Unauthorized, Content: Forbidden, IP Address: x) from Mailgun regarding forbidden IP Address are caused by certain IP Addresses needing to be whitelisted. Mailgun has the following troubleshooting guide that gives you step-by-step instructions on allowing certain IP Addresses.
Please take note of the addresses displayed in the error message as each Mailgun server is different and won't be the same for everyone.
Domain is not allowed to send
Errors (Unable to Send Despatch Email to: x Error:Unable to send Email. Exception: MailGun - Unable to Send Email, Status: Forbidden, Content: {"message":"Domain x is not allowed to send: x"} , IP Address: x) from Mailgun mentioning Domain x is not allowed to send typically provide a reason, such as Subscription Cancelled, the domain is unverified and requires DNS configuration, among others.
These must be actioned before emails will start sending again from Mailgun.