I try to migrate a spring-boot 3 project from

 <dependency>
        <groupId>com.sun.mail</groupId>
        <artifactId>javax.mail</artifactId>
        <version>1.6.2</version>
 </dependency>

to recent version of Jakarta

 <dependency>
        <groupId>com.sun.mail</groupId>
        <artifactId>jakarta.mail</artifactId>
        <version>2.0.1</version>
 </dependency>

I have a problem here.

 MimeMessage mm = null;
 SMIMEToolkit tk = new SMIMEToolkit (new BcDigestCalculatorProvider ());
 tk.isEncrypted (mm);  // expects a Part now

isEncrypted expected a MimeMessage before with javax. Now with Jakarta it is a part.
How can I get a part out of my existing MimeMessage?

SMIMEToolkit is out of

<dependency>
        <groupId>org.bouncycastle</groupId>
        <artifactId>bcmail-jdk18on</artifactId>
        <version>1.78</version>
</dependency>