It is not that difficult really. If VM mark or identify and e-mail as spam the web mail platform will not allow you to forward it on "as is". VM do not wish to be party to knowingly sending spam through their servers.
However the spam filter is at best capricious and this rule will apply equally to mail mark or identified erroneously as spam.
There is a work round involving the use of an e-mail client and adding the offending mail as an attachment which disguises it from the servers.
We have pointed out the difficulty all this causing to users and we have asked for the platform to behave sensibly and let users do what they wish to do - including sending spam, like phishing e-mails, to the abuse address of the organisation that appears to have sent it.
You should also read this, and not change back from this default which guarantees that you will receive all the mail intended for you:
Superuser 2017/18 Use Kudos to say thanks Mark answer as "helpful" only when the problem is solved Please don't send me private messages unless I ask you to. I do not work for VM. The advice I give is based on my best understanding of VM policy and practice. You rely on it at your own risk.