RSASSA-PSS p1v2.1 (rfc 4056) signing I'm signing mails with the RSASSA-PSS (p1v2.1) certificate. When I click Details, it shows &quot;Signature Algorithm: RSASSA-PSS&quot;.
openssl x509 -text shows
    Signature Algorithm: rsassaPss
     Hash Algorithm: sha256
     Mask Algorithm: mgf1 with sha256

certutil -dump shows:
1.2.840.113549.1.1.10 RSASSA-PSS

Now, whem I send my signed emails and click on Details in outlook, it shows &quot;Signature Algorithm: RSA (2048)&quot;
I'm using bouncycastle for signing and when I use &quot;SHA256WithRSAEncryption&quot; it works fine, but when I'm using &quot;SHA256WithRSAAndMGF1&quot; Signature, Outlook tells me &quot;The digital signature on this item is Invalid or Not Trusted.&quot; and when I click details, I see &quot;Signature Algorithm: RSA (2048)&quot;.
Is p#1v2.1 still not supported by outlook/microsoft or am I just crazy?
Is p#1v2.1 still not supported by outlook/microsoft or am I just crazy?

PSS seems still not introduced to Microsoft, please see here. It's a long discussion, but in the end it seems that you cannot select PSS as a signature scheme when sending, I presume that also means that PSS signatures are not accepted.
RSA-OAEP based encryption is generally supported earlier than PSS. There are padding oracle attacks against the PKCS#1 v1.5 encryption scheme. The PKCS#1 v1.5 signature scheme is still considered secure, so there is much less need for upgrading it.