Issues with mail.riseup.net:587 X.509 Cert

since today, I'm getting this when trying to send email via msmtp:

msmtp: TLS certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.

and I'm getting this with openssl s_client:
$ openssl s_client -showcerts -servername mail.riseup.net -connect mail.riseup.net:587
CONNECTED(00000003)
140199653545216:error:1408F10B:SSL routines:ssl3_get_record:wrong version number:../ssl/record/ssl3_record.c:331:
---
no peer certificate available
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No client certificate CA names sent
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SSL handshake has read 5 bytes and written 307 bytes
Verification: OK
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---

any idea?

thanks,

-- S