Setting access permissions to enclosed files for a NAS

Question

I'm using Ubuntu 16.04 Lts and a NAS (Synology, but I don't think the brand is relevant to my issue) where I backup my data and shares synced files with others. My NAS synced files and folders from two different locations in my computer:

• home : /home (my default hdd in ubuntu)
• Data : /media/'myusername'/Data : which is a mounted hdd on which I store data.

Everytime I reboot my computer the syncing software has trouble because it does not have sufficient access permission to sync files in Data (There is no issue to access home).

So I went to change permission (in property of Data) to give Create and Delete permissions to others. It worked until I reboot my computer. Then, the "not sufficient access permission" came back. I went back to the permission setting, the "Create and Delete permissions to others" was already activated, however, I had this time to change in "Change permissions for enclosed files" "Others : Read & Write + Create and delete files". And I have to do this every time I reboot my computer.

I have two related questions:

• how can I give access to this syncing software so that I don't have to change manually permission every time ?
• is there a more secure way to do it than giving all access and permission to "others" ? (I don't know why, but I feel there should be a way to say I only give these permission to the syncing software (Synology cloud station rather than every other users)

Thank you !