This is still happening after a reboot, Fedora 28. Restarting dovecot fixes the problem. Does anyone know if it could be related to this bug report? https://bugzilla.redhat.com/show_bug.cgi?id=103401#c130 and suggested work around to add ports to /proc/sys/net/ipv4/ip_local_reserved_ports?
Nov  8 12:21:41 ourdomain dovecot[1386]: Error: service(pop3-login): listen(*, 995) failed: Address already in use
Nov  8 12:21:41 ourdomain dovecot[1386]: Error: service(pop3-login): listen(::, 995) failed: Address already in use
Nov  8 12:21:41 ourdomain dovecot[1386]: Error: service(imap-login): listen(*, 993) failed: Address already in use
Nov  8 12:21:41 ourdomain dovecot[1386]: Error: service(imap-login): listen(::, 993) failed: Address already in use

dovecot --version
2.2.36 (1f10bfa63)

dovecot -n
# 2.2.36 (1f10bfa63): /etc/dovecot/dovecot.conf
# OS: Linux 4.18.16-200.fc28.x86_64 x86_64 Fedora release 28 (Twenty Eight)
# Hostname: ourdomain.com
auth_debug = yes
debug_log_path = /var/log/dovecot-debug.log
mail_debug = yes
mbox_write_locks = fcntl
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
}
passdb {
  driver = pam
}
ssl = required
ssl_cert = </etc/letsencrypt/live/ourdomain.com/fullchain.pem
ssl_cipher_list = PROFILE=SYSTEM
ssl_key =  # hidden, use -P to show it
userdb {
  driver = passwd
}
protocol imap {
  mail_location = mbox:~/mail:INBOX=/var/mail/%u