Begin by familiarizing yourself with the Postmark API documentation. Postmark provides APIs that allow you to access your email data. You will need to know how to authenticate and make requests to retrieve the data you need, such as email logs, bounces, or other relevant information.

Obtain your Postmark API token from your Postmark account settings. This token is required to authenticate your requests to the Postmark API. Ensure you keep this token secure and do not expose it in your code or documentation.

Use a programming language of your choice (such as Python, JavaScript, or PHP) to write a script that makes HTTP GET requests to the Postmark API endpoints. For example, you can use Python's `requests` library to fetch email logs. Ensure your script handles pagination if necessary, as the API might return large sets of data.

```python
import requests

API_TOKEN = 'your-postmark-api-token'
headers = {'X-Postmark-Server-Token': API_TOKEN}
response = requests.get('https://api.postmarkapp.com/email/message', headers=headers)

if response.status_code == 200:
data = response.json()
# Process your data here
else:
print('Failed to retrieve data:', response.status_code)
```

Once you have retrieved the data from Postmark, transform it to match the schema of your MySQL destination. This may involve mapping fields from the Postmark data to your MySQL table columns, converting data types, or cleaning up the data to fit your destination schema requirements.

Use a MySQL client library appropriate for your programming language to establish a connection to your MySQL database. For Python, you might use `mysql-connector-python` or `PyMySQL`. Install the required package and configure your connection parameters, such as host, user, password, and database name.

```python
import mysql.connector

connection = mysql.connector.connect(
host='your-mysql-host',
user='your-username',
password='your-password',
database='your-database'
)
```

Write a script that inserts the transformed data into your MySQL database. Use prepared statements or parameterized queries to prevent SQL injection and ensure data integrity. Handle any potential exceptions that might occur during the insertion process.

```python
cursor = connection.cursor()
insert_query = """
INSERT INTO your_table (column1, column2) VALUES (%s, %s)
"""
for item in data:
cursor.execute(insert_query, (item['field1'], item['field2']))

connection.commit()
cursor.close()
```

Once your script is tested and working correctly, automate the data transfer process by scheduling it to run at regular intervals. You can use tools like `cron` on Unix-based systems or Task Scheduler on Windows to execute your script periodically, ensuring that your MySQL database is updated with the latest data from Postmark.

By following these steps, you can effectively move data from the Postmark app to a MySQL destination without relying on third-party connectors or integrations.