The DCC features are all enabled by default.
Use the -M flag to disable the DCC blacklist (filename mangling), which will otherwise reject files with suspicious-looking names. Which file names are actually on the list can be configured at compile time or using the TCP wrapper support.
Use the -S flag to disallow all DCC file transmissions.
Use the -C flag to disallow DCC chat.
Use the -U flag to disallow other (unknown) kinds of DCC.
The implications of these options are discussed in more detail in the chapter about IRC basics and the Tircproxy feature overview.