Mail to accounts being blocked

Just a heads up that I found out today that mail from our mail server is being rejected by mail servers.

One of my mail users was sending a message to a friend and it bounced with:

host[] said: 550 SC-001
(SNT0-MC4-F38) Unfortunately, messages from weren’t sent.
Please contact your Internet service provider since part of their network
is on our block list. You can also refer your provider to (in reply to MAIL
FROM command)

So I dutifully contacted our ISP for the mail server, ServerBeach, as well as hotmail. The ServerBeach folks (awesome as always) replied in minutes and said that the IP is not on any other blacklist, so I had to deal directly with hotmail. I got a reply from hotmail that the issue couldn’t be automatically mitigated, so I had to fill out another questionnaire on-line, and I assume I’ll have to wait a couple of days for it to be addressed.

The funny part is that I looked through our logs, and we’ve tried to send exactly five e-mail messages today to hotmail addresses. Two were to the legitimate address that started this whole process, and three were to addresses like:

which appear to be spammers trying to register on our wiki. The wiki replies and requires an additional action in order to register, and I assume it is this mail traffic that is causing the problem. Note that all of our mailing lists are handled by Sourceforge so this only affects mail from the wiki, project members and employees of OpenNMS.

I think it is pretty ironic that the reason my mail server is being blocked by hotmail is that spammers from hotmail are trying to register on our wiki.

Update: Surprise – I got a rather quick reply from hotmail:

My name is Amrita and I work with the Hotmail Deliverability Support Team.

Your IP ( was blocked by Hotmail because Hotmail customers have reported email from this IP as unwanted. I have conducted an investigation into the emails originating from your IP space and have implemented mitigation for your deliverability problem. This process may take 24 – 48 hours to replicate completely throughout our system.