@cwebber we trouble shooted some of this stuff for cybre.space email once, https://sendersupport.olc.protection.outlook.com/pm/postmaster.aspx has a bunch of info and you can open a support ticket here: https://support.microsoft.com/en-us/getsupport?oaspworkflow=start_1.0.0.0&wfname=capsub&productkey=edfsmsbl3&locale=en-us&forceorigin=esmc&ccsid=636646882994071110
@nightpool Thanks... I didn't know about that form. Filed one with it. Hopefully it helps...
@cwebber definitely check out what SMTP error code you're getting, there's a whole list of them on this page: https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx
@cwebber IIRC when it started happening to us, it was because our registrar's nameserver completely mangled our SPF records :O
@nightpool It looks like they're blocking a whole network, probably Linode machines in my vacinity.
@nightpool based on the error message
@cwebber when this happened to us all we had to do was fill out the form and they whitelisted us