mail out called spam

Can not send outgoing.  Error message is: Your message did not reach some or all of the intended recipients.        Subject:    test here       Sent:    8/24/2016 9:52 PM  The following recipient(s) could not be reached:        ‘’ on 8/24/2016 9:52 PM             550 5.7.1 Spam detected by content scanner.  Message rejected.

I spoke with optonline support and they say it is not anything they are doing.

What/where/who is “content scanner” that has rejected my outgoing messages?

Beats me, but it certainly is not emclient

Thanks.  I read somewhere that there is an IP Address Spam List/Lists.  Have you any idea who maintains it/them and how I can get it reviewed?