I can't send mail about abuse/phishing

[#1]

I tried to send a message to abuse@123-reg.co.uk concerning a phishing abuse site hosted by them but I can't send the mail because PlusNet reject the mail with this message.
[15:05:12] SMTP< 552 nT5B1k0012U56wP01T5Cq2 message rejected due to spam or virus. If you believe this is in error please login to your portal or contact your ISP support team.
** error occurred on SMTP session
*** Error occurred while sending the message:
552 nT5B1k0012U56wP01T5Cq2 message rejected due to spam or virus. If you believe this is in error please login to your portal or contact your ISP support team.
Now what do I do?  Message is plain text has has no links embedded.

[#2]

To enable you to forward that Plusnet would have to whitelist the 123-reg abuse address. You would need to raise a ticket to request that. Alternatively if you have a gmail (or similar) account you could try using their SMTP server.

[#3]

OK.  Thanks for that.