Update mail connector dependencies

[martingrossmann]

Description

The mail connector dependencies were updated:

• Latest Jakarta Mail, results in latest transitive dependencies
• Latest Bouny Castle Mail for Jakarta
• Removed outdated Base64 lib

Fixes #290

Important note

Some packages were changed in Jakarta Mail 2.0.1. Can be updated by search-and-replace.

// Jakarta Mail 1.6.x
import javax.mail.Message;
import javax.mail.internet.MimeBodyPart;
import javax.mail.search.AndTerm;
import javax.mail.search.SearchTerm;
...

// Jakarta Mail 2.x
import jakarta.mail.Message;
import jakarta.mail.internet.MimeBodyPart;
import jakarta.mail.search.AndTerm;
import jakarta.mail.search.SearchTerm;
...

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules