Well I emailed RR security and asked them about blocking mail to SC. I was in contact with a person who actually was knowledgeable and informative. After giving him some specific times and dates for emails being blocked he tracked them down in the logs and found that yes they were found to contain spam and were discarded.
RR is scanning both incoming and outgoing emails for spam. Incoming you can use a webmail interface and stop the inbound filtering or control the degree of filtering. Outgoing however has no such control. They do acknowledge that they are just discarding outgoing spam mails as the system has no other option at this time. I will post a sanitized version of their response below.
I got the answer to you problem here; I'm not sure how you'll respond, but please read this in its entirety...
As you may be aware, xxx.rr.com users were migrated to a new mail system last week. Unlike the old mail system you had been hosted on, this new system has, in addition to our block lists, filtering of email based on spam-like characteristics in the body. This filtering is occurring on both inbound and outbound mail.
Inbound mail identified as spam by this filtering software is placed into the customer's spam Folder; this folder is accessible only through webmail (https://webmail.xxx.rr.com/). Our webmail product in this new system also offers a 'Report spam' button.
For outbound mail, obviously we cannot tag a message deemed to be spam by our own systems and send it along to the destination; doing so would cause us to be viewed in a bad light by the rest of the Internet.
While the optimal configuration for outbound spam filtering is to identify the message as spam during the SMTP transaction between the client and our server, and to reject the message before the transaction completes, our server technology at this time does not allow for such configuration. Therefore, we are discarding messages identified as spam on our outbound servers.
Your particular message to SpamCop was identified as spam and discarded; timestamps here are GMT:
Removed Header info:
The choice to do this (identify and discard) was not made lightly, but the alternative of allowing spam out through our servers was not acceptable; in fact, we learned early on with this new system the pain of delays and outright rejections of outbound mail from the new system due to a lack of spam control. Cutting down the flow of spam through our servers by discarding messges deemed to be spam was the best approach available to us at the time in order to give our customers the best chance of having their outbound mail accepted and delivered.
If you're wondering why this message ever made it to your Inbox (i.e., why didn't the spam filtering catch it inbound, since it knew about it
outbound) I cannot answer that question. My suspicion is that, given the timing of things, it was delivered initially to you Inbox on the old system, migrated with the rest of your mailbox contents to the new system, and then you tried to send it out through the new system; the headers of the particular message will confirm or deny my suspicions.
We're still in the early stages of deployment of this mail system, and we recognize that today's configuration is not likely to be the final configuration; tweaks to our anti-spam software are going to be necessary, and we'll work hard to figure out what the right tweaks are.
I hope this answers your question, but feel free to ask any follow-on questions you may have.
Maybe SC might give RR a hand. I asked them to look into allowing SC to be unfiltered but to limit emails by number and time if possible, but have not heard back from them.
Anyway, just some info should you find your emails to SC disappearing.