Some delivery agents, such as those that deal with files, require that the recipient's hostname be left as is. The hostname portion of the recipient's address is ordinarily converted to lowercase before being tucked into $h. Specifying the F=h delivery agent flag tells sendmail to not convert that address to lowercase.^[30]

^[30] This delivery agent flag was added specifically to handle the UUCP host named Shasta at Stanford University.

The $h sendmail macro ($h) is usually used with the A= delivery agent equate of a delivery agent. For example:

Muucp, P=/usr/bin/uux, F=msDFMh uU, A=uux - -r $h!rmail ($u)
                               
                             note

Here, the h in F=msDFMhuU tells sendmail to leave the $h alone and not to convert the hostname in that sendmail macro to lowercase.