I had this problem about a year ago.
“Unfortunately, messages from [135.181.139.185] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3150).”
Can you resolve thus urgently please…
Regain your privacy! Adopt /e/OS the unGoogled mobile OS and online services
I am experiencing the same since yesterday. If I interpret @Manoj’s answer on this issue, all we can do is indeed report and wait for /e/ to get in touch with Microsoft and then for Microsoft to solve the issue.
This was the issue last time:
It got fixed fairly quickly. Suspect Microsoft is desperate for custom.
I still (again?) have this issue, three weeks seems like a long time to get this fixed, no?