you are in emergency mode
solution: check /etc/fstab for any invalid mounting
postdrop: warning: uid=0: File too large
postdrop: warning: uid=0: File too large
sendmail: fatal: root(0): message file too big
Error sending message, child exited 75 (Deferred.).
Could not send the message.
solution: add the following parameter to configuration file
# vi /etc/postfix/main.cf
message_size_limit = 102400000 ### 100M
mailbox_size_limit = 102400000 ### should not lesser than message_size_limit, otherwise the entries in /etc/aliases will not work
# systemctl stop postfix
# systemctl start postfix