Hi,
You can move Outlook OST to Gmail by using Auto-Archive option. This method provides an option to select the number of days for which you need to archive the data. Follow the steps mentioned below:
1. Open your Microsoft Outlook account.
2. Click on Tools and select Options.
3. Select the Auto-Archive option from the given dialog box. Click on OK.
4. From Run Auto-Archive after every option and select the number of days required to archive the data.
5. Browse a location to save the Auto-Archive file. Click OK.
Once the Outlook OST files are converted into PST format you can easily import that converted data to Gmail with the help of the GAMMO tool.
Feel free to ask for further assistance.