View postfix queue:

# mailq

View message header and content:

# postcat -q <ID>

Delete specific mesage from queue:

# postsuper -d <ID>

Delete all mails from queue:

# postsuper -d ALL

Delete all mails in the defered queue:

# postsuper -d ALL deferred

Requeue all mails:

# postsuper -r ALL

Requeue all deferred emails:

# postsuper -r ALL deferred

a few more hints over here

If anyone is interested, using the command line mode in Clonezilla, I removed the GPT components using gdisk:

# sudo gdisk /dev/sda
GPT fdisk (gdisk) version 0.7.2

Partition table scan:
MBR: MBR only
BSD: not present
APM: not present
GPT: corrupt

Found valid MBR and GPT. Which do you want to use?
1 – MBR
2 – GPT
3 – Create blank GPT

Your answer: 1
Command (? for help): x

Expert command (? for help): z
About to wipe out GPT on /dev/sda. Proceed? (Y/N): y
GPT data structures destroyed! You may now partition the disk using fdisk or
other utilities.
Blank out MBR? (Y/N): n <— do NOT choose Y!
MBR is unchanged. You may need to delete an EFI GPT (0xEE) partition
with fdisk or another tool.

answer copied from this thread.

Here a a small summary of all invoked FreeBSD commands if you want to upgrade from let's say 11.0 to 11.1. All this info can also be found in the FreeBSD handbook.

First update your current version to the latest packages and reboot:

# freebsd-update fetch install
# pkg upgrade (command for binary packages)
# portmaster -a (command for installed ports, WARNING: see below)
# reboot

Warning for portmaster: portmaster will recompile also your binary packages if the port version is newer!

Now let's start the upgrade process:

# freebsd-update -r 11.1-RELEASE upgrade (replace 11.1-RELEASE with the upgrade version you want)
# freebsd-update install
# reboot
# freebsd-update install
# pkg-static upgrade -f (command for binary packages)
# portmaster -af (command for ports. WARNING: see above)
# freebsd-update install
# reboot

That's it. upgraded version up and running.