US SMTP server blacklisted by Microsoft
Friday 24th January 2020 14:15:00


Our US SMTP service is currently on Microsoft's blacklist. Messages sent to email addresses that use Microsoft's email services (including hotmail.com and outlook.com) may be bounced back to their original sender.

We're working with MS to have the server de-listed and will update this incident when it is done.

Microsoft has continued to be unresponsive to our inquiries, leaving us no recourse except to move our US SMTP to a new IP address.

We will begin the transition on Monday April 6 at 3AM UTC (2020-04-06 03:00 UTC).

We anticipate that this transition will be minimally disruptive (if at all) and will not require any changes to customer mail client settings.

If you notice any problems sending mail during or after the transition, please contact our support team for assistance.

Microsoft has been unresponsive to our inquiries for the past week so we've opened a new ticket with them.

According to Microsoft's own postmaster tools the US SMTP is not blacklisted and no spam-like activity has been detected since 29 January 2020 - however, we're still seeing bans for mail sent from the US SMTP to domains that use Office 365 email.

We'll continue to work with MS to get this resolved. In the meantime, customers affected by this issue can work around it by creating a new mail user on our Frankfurt, Germany mail server and using that user for their SMTP authentication for outgoing mail.

https://sender.office.com/ is reporting that our SMTP is no longer blocked but we're still seeing intermittent bans in our mail logs. We've reached out to Microsoft for an update and are awaiting their response.

This issue is ongoing. We'll continue to work towards resolution.

Microsoft has once again assured us that our US SMTP has been removed from their blacklist. We'll continue to monitor.

We are still seeing ban activity In spite of the assurance from Microsoft that our US SMTP was removed from their blacklist. We'll continue to work with them to get this resolved.

Microsoft has delisted our US SMTP as of approximately 2:15 PM UTC 31 Jan 2020. It may take another couple of hours for the delisting to take full effect, so we will continue to monitor.

This issue is ongoing. We've taken all of the required actions as dictated by Microsoft so far and are waiting for them to delist the server.

In the meantime if you are a US customer affected by this block, feel free to use our German SMTP server to send mail: smtp.de.opalstack.com