In mutt and neomutt, PGP encryption does not use the --hidden-recipient mode which may leak the Bcc email header field by inferring from the recipients info.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:LI:NA:N5.3/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:NOther