The email provider Securence (US Internet, now owned by a joint venture between T-Mobile and KKR) has disabled its administrative portal for a week now, although email is still flowing. The company won't say the cause or share much about what's happening. Believe me, I've tried.
This is the same company that published more than a decade's worth of customer (and internal company) emails in plain text on the web a couple years back.
https://krebsonsecurity.com/2024/02/u-s-internet-leaked-years-of-internal-customer-emails/