mailq — stdin stdout - file -- opt --help --version
mailq command lists any
outgoing email messages awaiting delivery.
$ mailq Queue ID- --Size-- ----Arrival Time-- -Sender/Recipient--- 46AAB43972* 333 Tue Jan 10 21:17:14 email@example.com firstname.lastname@example.org
Sent mail messages are also recorded in a log file such as /var/log/maillog; the name may differ from distro to distro.