Begin by logging into your Mailjet account and navigating to the section where your emails or campaign data is stored. Use the export functionality to download the data as a CSV or Excel file. This usually involves selecting the data you wish to export and choosing the format for download. Save the file to your local machine.

Open the exported file using a spreadsheet application like Microsoft Excel or Google Sheets. Review and clean the data, removing any unnecessary columns or rows. Ensure that the data is organized in a way that aligns with the schema of your Oracle Database. Rename columns if necessary to match the database table columns.

Make sure you have access to the Oracle Database where the data will be imported. This involves having the necessary credentials such as username, password, and database connection details (host, port, and service name). Test your connection using an SQL client like SQL*Plus or SQL Developer to ensure you can access the database.

If the table where you want to import the data doesn't exist, you’ll need to create it. Use the SQL client to execute a CREATE TABLE statement with the appropriate schema that matches your prepared data. For example:
```sql
CREATE TABLE mailjet_data (
id NUMBER,
email VARCHAR2(255),
subject VARCHAR2(255),
date_sent DATE,
...
);
```

With the data prepared, convert it into a format suitable for SQL insertion. This can involve scripting to create SQL INSERT statements for each row of data in your CSV or Excel file. Here’s a Python snippet example:
```python
import csv

with open('mailjet_data.csv', 'r') as file:
reader = csv.reader(file)
for row in reader:
print(f"INSERT INTO mailjet_data VALUES ({', '.join(row)});")
```
This will output SQL commands that can be executed in your Oracle Database.

Copy the generated SQL INSERT statements into your SQL client tool connected to the Oracle Database. Execute these statements to insert the data into your target table. Ensure that all data types match the column definitions (e.g., dates are in the correct format).

After importing the data, run a series of SELECT queries to verify that the data was transferred correctly. Check for any discrepancies or errors during the import process. If any issues arise, troubleshoot accordingly by comparing the source data with the database entries. Make any necessary adjustments to the data or SQL scripts and re-import as needed.

Following these steps will help you manually move data from Mailjet emails to an Oracle Database without the need for third-party connectors or integrations.