tl;dr: Before contacting Microsoft about problems sending email to @hotmail.com addresses, check your IP address' reputation with Symantec here.
When setting up a new VPS you sometimes discover that the IP address you have been given is blacklisted or has a negative reputation, perhaps because the previous tenant was spamming or hosting a compromised website with malware. This is obviously a problem if you plan to send email from the VPS.
The procedure for getting an IP delisted varies depending on which list it is on. In some cases it isn't worth the trouble, e.g. if the IP is on a little used list, or if the list owner charges a fee for delisting. But if your IP is being blocked by one of the large freemail providers - Gmail, Hotmail, Yahoo mail - you will probably want to get off their blacklist as quickly as possible.
After creating a new VPS on Vultr.com we discovered that emails sent to hotmail.com addresses were bouncing with the following error message:
host mx4.hotmail.com [18.104.22.168] SMTP error from remote mail server after MAIL FROM:<email@example.com> SIZE=1895: 550 OU-002 (COL004-MC3F9) Unfortunately, messages from 108.xxx.xxx.xxx 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 http://mail.live.com/mail/troubleshooting.aspx#errors.
A quick check with MX Toolbox showed that the IP was not listed on any of the publicly queryable blacklists, so we started looking for a way to contact Microsoft with our problem.
Microsoft publishes various general information about their email and spam policies, but it can be difficult to find actual information about how to contact them about delivery problems. We eventually found our way to this "Sender Information for Outlook.com Delivery" form.
About 10 minutes after filling in and submitting the form we got the following email response:
Dear Tom Risager Please note that your ticket number is in the subject line of this mail. 108.xxx.xxx.xxx Note: Errors are unlikely, however, if an error is indicated, please resubmit the specific IP or IP range. Thank you, Outlook.com Deliverability Support Please do not reply to this message as it is from an unattended mailbox. Any replies to this email will not be responded to or forwarded. This service is used for outgoing emails only and cannot respond to inquiries.
This had us scratching our heads a bit, especially the Note: Errors are unlikely, however, if an error is indicated, please resubmit the specific IP or IP range part. We eventually decided that our delisting request had been rejected, so we filled in and submitted the form again.
This time we had to wait about half an hour before we got the following:
Dear Tom Risager We have completed reviewing the IP(s) you submitted. The following table contains the results of our investigation. More information needed 108.xxx.xxx.xxx Our investigation has determined these IP(s) are being blocked based on the recommendations of Symantec's BrightMail filter. We will be happy to work directly with Symantec on your behalf to investigate and possibly resolve this problem. Symantec will re-evaluate your IP and remove the block if appropriate. Please note that even if the block is removed, it does not guarantee that your email will be delivered to a user’s inbox. Typically, Symantec has a response within 5 business days. After then, if your issue is not yet resolved, please reply to this email and one of our support team members will contact you for further investigation. Please reply to this email and one of our support team members will contact you for further investigation. ... (a lot of general information about email delivery omitted) ... Thank you, Outlook.com Deliverability Support
Again some confusion at our end. It seemed that we should either wait five business days for the issue to be resolved, and then contact the support team if there was still a problem. Or perhaps we should contact the support team first with additional information, before they would take any action? Also, the email was sent from the same address as the first one which explicitly stated that it was sent from an unattended mailbox, but no other contact email address was provided.
We didn't feel like waiting five business days without doing anything, so we sent a reply with a brief recap of our issue - hoping that it would eventually get back to a human being, and that our description would cover the "more information needed " bit.
Looking at the second email again we realized that there might be another way - perhaps we could solve the problem by going directly to Symantec. After a brief search we found our way to Symantec's IP Reputation Investigation page. A lookup confirmed that our IP did indeed have negative reputation with Symantec, so we sent a delisting request via the form.
Symantec promises to process delisting requests within 24 hours - much better than the five business days quoted by Microsoft - but it took much less time than that. An individual from Hotmail Sender Support responded to our email about three hours after our initial contact with Microsoft, but only to say that he could not see any issues with our IP. A quick check confirmed that the IP no longer had a negative reputation with Symantec and that we could now send email to Hotmail addresses. Yay!
(Dear Microsoft: Responding within three hours to our delisting request was excellent support. But why make it so hard to find the reporting form, and please do something about those emails).