You're almost there; you just need to add a
statement at the top of your code file, above the interface declaration.
Alternatively, you could do
Public Class clsOracleDisEmail
On a small, very pedantic note, Microsoft recommended best practice is for your interfaces to start with and I, so instead of having _clsOracleDisEmail you'd have something like IOracleDisEmail. However, it's your code so you do what you like!
Also, to get rid of all compiler warnings, I had to add a reference to ADODB, because of the ADODB.Connection parameter in the Send method.