If you would rather allow osTicket to fetch all mail, you probably just need to increase the file upload size limit in your php.ini.
On the server command line, run php --ini
If your server is Windows, you may need to cd path\to\php.exe
In the output you should see which php.ini your crontab/task is using. This may be different from the config that your web site uses.
For example:
Loaded Configuration File: /etc/php/8.0/cli/php.ini
Edit the file and find: upload_max_filesize. The default is 2m.