In May, Newshub exposed a number of Lyttelton Port Company employees' serious concerns.
The mail is believed to be related to a string of personalised attacks.
Thousands of people experience bullying every year in New Zealand.
"It is something that will be with me for the rest of my life."
An expert details the harm of not identifying better ways of working with each other.
A leading advocate says it's one of New Zealand's last taboos.
"It is not okay for people to go to work, and be harmed because of the job they do."
On Monday afternoon, LPC chief executive Roger Gray announced an independent investigation will go ahead.
Current and former employees have spoken out about LPC's practices.