Can I update Mac OS 10.11 to 10.11.6 using a dmg of the update?
You can get the dmg file from here: https://support.apple.com/downloads/macos

While downloading the dmg please check the system requirement. Because you will need a combo dmg file if you are upgrading from say 10.11 to 10.11.6

On detail page of the dmg there is a System Requirements button at the bottom, please check the system requirement from there.

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Source: Ask Different