Some delivery agents don't correctly understand quotation marks in addresses. For example:

"dechost::user"@relay

For delivery agents that do not correctly understand them, the F=s delivery agent flag causes sendmail to strip all quotation marks from the address before handing it to the delivery agent:

dechost::user@relay

The local delivery agent should always have the F=s delivery agent flag specified. The prog delivery agent commonly has the F=s delivery agent flag specified. The uucp delivery agent might or might not require that delivery agent flag, depending on the specifics of the program specified in the P= delivery agent equate. The [IPC] delivery agents should never specify the F=s delivery agent flag.