Here is the returned events log on my machine.
tell application "Mail"
activate
delete mailbox "Year 2016"
make new mailbox with properties {name:"Year 2016"}
say "Mail box Year 2016 created."
«event ascrgdut»
say "Mail box Year 2016 created."
end tell
tell current application
say "Mail box Year 2016 created."
end tell
tell application "Mail"
make new mailbox at beginning of every mailbox of mailbox "On My Mac/Year 2016" with properties {name:"Year 2016/11"}
say "Mail box 2016 11 try 2 failed to be created"
end tell
tell current application
say "Mail box 2016 11 try 2 failed to be created"
end tell
tell application "Mail"
make new mailbox at beginning of every mailbox of mailbox "Year 2016" with properties {name:"Year 2016/11"}
say "Mail box 2016 11 try 3 failed to be created"
end tell
tell current application
say "Mail box 2016 11 try 3 failed to be created"
end tell
tell application "Mail"
make new mailbox at mailbox "Year 2016" with properties {name:"Year 2016/11"}
say "Mail box 2016 11 try 4 failed to be created"
end tell
tell current application
say "Mail box 2016 11 try 4 failed to be created"
end tell
tell application "Mail"
make new mailbox with properties {name:"Year 2016/11"}
say "Mail box 2016 11 try 5 failed to be created"
end tell
tell current application
say "Mail box 2016 11 try 5 failed to be created"
end tell
tell application "Mail"
make new mailbox at beginning of every mailbox of mailbox "Year 2016/11" with properties {"2016 11 17"}
say "Mail box 2016 11 17 try 6 failed to be created"
end tell
tell current application
say "Mail box 2016 11 17 try 6 failed to be created"
end tell
Mailbox 2016 was created but every other instructions failed.
It seems that it would have been a good idea to type « tell me to « before « say ».