This format strings specifies a command which is used to decode application/pgp attachments.
The PGP command formats have their own set of printf-like sequences:
Expands to PGPPASSFD=0 when a pass phrase is needed, to an empty string otherwise. Note: This may be used with a %? construct.
Expands to the name of a file containing a message.
Expands to the name of a file containing the signature part of a multipart/signed attachment when verifying it.
The value of $pgp_sign_as.
One or more key IDs.
For examples on how to configure these formats for the various versions of PGP which are floating around, see the pgp*.rc and gpg.rc files in the share/examples/mutt subdirectory which has been installed on your system. (PGP only)