[Client-to-Server] create .mbox parser

[Jonas-Karl]

Description As a user I want access to my received and send Emails. This can be achieved by adding a Database which stores the .mbox files.

Ready Criteria

• [ ] everyone understood the scope of this ticket
• [ ] effects in domain- / useCase- / external-layers are discussed
• [ ] atleast one person is assigned
• [x] example .mbox exists

Acceptance Criteria ( - [x] reading is only possible when logged in) This will be done in the future

• [x] reading the mbox file allows to retrieve a list of Emails
• [x] good case tests are written
• [x] bad case tests are written

Scope ✅ .mbox parser ❌ .mbox generator

Additional context Add any other context or screenshots about the feature request here.

[Jonas-Karl]

This will now be implemented in json instead of mbox