Edit: /etc/mail.rc (1909B)
# This is the configuration file for Heirloom mailx (formerly
# known under the name "nail".
# See mailx(1) for further options.
# This file is not overwritten when 'make install' is run in
# the mailx build process again.
# Sccsid @(#)nail.rc 2.10 (gritter) 3/4/06
# Do not forward to mbox by default since this is likely to be
# irritating for most users today.
set hold
# Append rather than prepend when writing to mbox automatically.
# This has no effect unless 'hold' is unset again.
set append
# Ask for a message subject.
set ask
# Assume a CRT-like terminal and invoke a pager.
set crt
# Messages may be terminated by a dot.
set dot
# Do not remove empty mail folders in the spool directory.
# This may be relevant for privacy since other users could
# otherwise create them with different permissions.
set keep
# Do not remove empty private mail folders.
set emptybox
# Quote the original message in replies by "> " as usual on the Internet.
set indentprefix="> "
# Automatically quote the text of the message that is responded to.
set quote
# Outgoing messages are sent in ISO-8859-1 if all their characters are
# representable in it, otherwise in UTF-8.
set sendcharsets=iso-8859-1,utf-8
# Display sender's real names in header summaries.
set showname
# Display the recipients of messages sent by the user himself in
# header summaries.
set showto
# Automatically check for new messages at each prompt, but avoid polling
# of IMAP servers or maildir folders.
set newmail=nopoll
# If threaded mode is activated, automatically collapse thread.
set autocollapse
# Hide some header fields which are uninteresting for most human readers.
ignore received in-reply-to message-id references
ignore mime-version content-transfer-encoding
# Only include selected header fields when forwarding messages.
fwdretain subject date from to
# For Linux and BSD, this should be set.
set bsdcompat