the error 552 5.7.0 SPAM Content Found (VM603)
As @Client62 has intimated, that VM603 error normally arises because the Virgin Media outgoing spam filters have flagged the contents of the email you are trying to send as spam. That suggests there is something triggering VM's spam filter, such as a suspicious URL perhaps in the email signature,
- either in your email,
- or possibly in the original email included with your reply email.
Rather bizarrely it seems quite common for VM's incoming spam filters to find no problem with the contents of an incoming email but when you reply to that email VM's outgoing filters then flag it as spam.
Out of interest I have just checked the domain fedcapemployment.org (and also the IP address of their email server) to see if they are listed on any blocklists. I checked here https://mxtoolbox.com/SuperTool.aspx (use the drop-down list to change from "MX lookup" to"Blacklist check" ) and here http://www.anti-abuse.org/multi-rbl-check-results/ and they do not come up on any of the many blocklists they check against.
Of course it is possible that VM has their own blocklist they use in conjunction with the many recognised ones. However, the VM603 error (or SMTP602 depending on whether you are using the VM webmail service or an email client to send the email) seem linked to the content of the message not its intended recipient.
One of the VM Forum Team (VM staff who support this forum) should be contacting you via this thread today or tomorrow. They are best placed to help you further if necessary.
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