My solution to the problem when Outlook, Hotmail and a bunch of other email domains from Microsoft blacklisted my Mailgun IP and blocked all emails.
What happened was that an account on the same shared Mailgun IP had sent a lot of emails to Outlook which had caused them to add the IP to their block list.
The solution was to email Mailgun and explain to them what had happened.
They were very helpful and quickly moved my Mailgun emails to another IP address, which wasn’t blocked. Although emails were delivered straight away, Outlook was marking the emails as spam and moving them to the junk folder.
The spam problem is solved over time as Outlook users mark emails as not junk.
No need to purchase a unique IP address. Also, I’ve set up a “Zapier automation” which integrates with Mailgun to notify of any future blocks.
The Microsoft email domains not working and doing the blocking were at least hotmail.com, outlook.com, msn.com and live.com.
Details on how the Mailgun emails were unblocked;
This was the error message in Mailgun logs;
5.7.1 Unfortunately, messages from [xxx.xx.xxx.xxx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [BN3NAM01FT008.eop-nam01.prod.protection.outlook.com]
Then I attempted to contact Microsoft, asking them to remove the blocked IP from their block list — the form to do that is under this link.
They responded that mitigation was not possible due to repeated violations of their policies, and so on. Oh well. So I emailed Mailgun;
Dear MailGun, All outgoing emails are being blocked by Live.com (Outlook, Hotmail, etc.), on the shared IP xxx.xx.xxx.xxx. I reported a deliverability problem to Outlook and they said that this IP is "Not qualified for mitigation", because "These IP(s) have previously received mitigations from deliverability support, and have failed to maintain patterns within our guidelines" Does this mean, that I cannot send emails to them with Mailgun for as long as I am using a shared IP address? Or is there something that can be done? My sending volumes are very low. Here's the log message: 5.7.1 Unfortunately, messages from [xxx.xx.xxx.xxx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [BN3NAM01FT008.eop-nam01.prod.protection.outlook.com] Best regards, David
To which Mailgun responded;
Hi There, Thank you for contacting Mailgun support, we are sorry to hear you are having issues with the shared IP assigned to your account. After review, it looks like a noisy sender on the IP caused it to become listed on a problematic blacklist. I've moved you to a new IP while we work on delisting the previous IP that was on your account. Please let us know if you have any questions, we are always happy to help! Thank You, Mailgun Support
My answer was;
Thank you very much. I successfully tested that mails are now going through to them, but looks like it’s going to the “junk email” box. But getting there…! Best regards, Teemu
They followed up;
Thanks for your update! Glad to hear of the improvement - make sure to have your recipients mark these messages as "Not Spam" to help train the metrics for their servers' filtering. I've gone ahead and modified your IP one more time to see if we can improve things a little more there, but the marking as "Not Spam" will help even more. Please let us know if you have any questions!
And that was the solution to the problem of getting blacklisted by Outlook.
Comments on Mailgun services are welcome.
Thanks for visit, and reading. David.