It doesn't exist. doveadm belongs in dovecot 2.x, but ubuntu only has 1.x versions.
Quoting Walt Shekrota <ws...@penguinacity.org>:
HiWhere does this utility reside for installation. I use Ubuntu and installed dovecot-imapd and dovecot-pop3d so far. Does it now ship in the regular dovecot installation packages?Thanks. -Walt