SMTP (DE) on Opalstack Status

[Resolved] smtp.de.opalstack.com rebooted for emergency maintenance

Mon, 01 Jun 2026 19:17:08 +0000

Fixed - The SMTP server is back online. (19:24 UTC — Jun 1)

We’ve just rebooted smtp.de.opalstack.com for emergency maintenance. We expect the server to be back online within the next few minutes. (19:17 UTC — Jun 1)

[Resolved] Unplanned emergencey maintenance on smtp2.de.opalstack.com

Fri, 23 Jan 2026 01:24:00 +0000

Fixed - There have been no further issues since our previous update. (15:03 UTC — Jan 24)

Fri Jan 23 00:56 UTC: SMTP2 DE became unreachable and has entered an emergency hardware maintenance state. In the interim, you may temporarily reconfigure your mail client SMTP settings to use smtp1.de.opalstack.com instead. Undates to domains in the dashboard may experience delays.

Fri Jan 23 01:35 UTC: The server became operational but more maintenance is required. No further downtime is expected but we will continue to monitor. (01:24 UTC — Jan 23)

[Resolved] Microsoft blocking mx1.us.opalstack.com and smtp1.de.opalstack.com

Sat, 16 Aug 2025 15:48:00 +0000

Fixed - The US MX block is now clear. (14:17 UTC — Aug 17)

Watching - The DE SMTP block has been cleared.

We’re still working with Microsoft to clear the US MX block. (17:37 UTC — Aug 16)

At this time mail sent from our DE SMTP server and mail forwarded from one of our US MX servers to outlook.com, hotmail.com, and live.com is being blocked by Microsoft. We’re working with Microsoft to correct the problem.

In the interim:

DE SMTP users can work around the SMTP block by configuring their clients to use smtp2.de.opalstack.com as their outgoing mail server.
US customers who use mail forwarding can work around the MX block by creating new MX records for mx2.us.opalstack.com with priority 5 and mx1.us.opalstack.com with priority 10. (15:48 UTC — Aug 16)

[Resolved] iCloud blocking US and DE SMTP

Thu, 26 Jun 2025 18:46:00 +0000

Fixed - The block was lifted as of 0600 UTC today. (21:19 UTC — Jun 27)

At this time Apple’s iCloud email service is blocking messages sent from our SMTP servers to Apple-hosted domains including icloud.com, me.com, and custom email domains that use the iCloud email service.

We’ve raised a ticket with Apple to determine the cause. (18:46 UTC — Jun 26)

[Resolved] DE SMTP blocked by iCloud

Mon, 03 Mar 2025 20:21:00 +0000

Fixed - The block was cleared as of 14:22 UTC today. Mail sent to iCloud email addresses via our DE SMTP are no longer bouncing. (17:40 UTC — Mar 7)

Identified - Apple informed us that our SMTP is caught up in a block of a larger IP address range operated by our network provider. Our provider is working with Apple to resolve the issue.

If you are affected by this you can configure your mail client to use smtp2.de.opalstack.com as its SMTP server as a temporary workaround. (20:53 UTC — Mar 5)

Identified - Apple informed us that our SMTP is caught up in a block of a larger IP address range operated by our network provider. Our provider is working with Apple to resolve the issue.

If you are affected by this you can configure your mail client to use smtp2.de.opalstack.com as its SMTP server as a temporary workaround. (20:44 UTC — Mar 5)

At the present time email sent to @icloud.com addresses via our DE SMTP server is being either deferred or bounced. We’re working with Apple to resolve the issue and will update this post when more information is available.

In the meantime, DE mail customers can work around the issue by using our alternate DE SMTP server in their email client settings. The alternate server is: smtp2.de.opalstack.com (20:21 UTC — Mar 3)

[Resolved] EU mail system blocked by Hotmail

Thu, 15 Feb 2024 15:21:00 +0000

Fixed - All blocks have been lifted. (03:30 UTC — Feb 16)

Watching - mx2.de.opalstack.com was added to the block list as well, we have submitted the delisting request and are awaiting action from Microsoft. (18:36 UTC — Feb 15)

Part of our EU mail infrastructure was blocked by Hotmail. The affected servers were:

smtp2.de.opalstack.com (outgoing mail)
mx1.de.opalstack.com (incoming mail and forwarding)

We’ve already dealt with the issue and Microsoft have confirmed that the servers have been unblocked, but it may take a few more hours to take full effect.

We’ll update this post when we’ve confirmed that mail is no longer being blocked. (15:21 UTC — Feb 15)

[Resolved] DE SMTP was blocked by Abusix

Fri, 20 Jan 2023 15:06:02 +0000

Fixed - The DE SMTP is no longer blocked. (20:08 UTC — Jan 20)

Our DE SMTP server was listed in the Abusix Mail Intelligence block list. We’ve already initiated the delisting process and expect the issue to be resolved within the next 60 minutes. (15:06 UTC — Jan 20)

[Resolved] DE SMTP blocked by Proofpoint

Mon, 09 Jan 2023 10:38:08 +0000

Fixed - The DE SMTP server is no longer blocked by Proofpoint. (18:24 UTC — Jan 10)

At this time our German SMTP server is being blocked by the Proofpoint blocklist. We’ve dealt with the cause and have started the de-listing process.

We’ll update this post when the server has been removed from the list. (10:38 UTC — Jan 9)

[Resolved] DE SMTP was briefly disrupted

Tue, 06 Sep 2022 14:52:06 +0000

The DE SMTP service was briefly disrupted due to a high load condition on the server. The problem is corrected and SMTP is working normally at this time. (14:52 UTC — Sep 6)

[Resolved] German SMTP blocked by Microsoft

Mon, 03 Jan 2022 21:40:00 +0000

Fixed - It’s been over a week and we’ve seen no blocks of the new server IP by MIcrosoft, so we consider this to be resolved. (15:04 UTC — Jan 17)

Watching - We informed Microsoft of our findings and the corrective action we’ve taken but we’ve still received no further communication from them.

To work around this we’ve moved smtp.de.opalstack.com to a new IP address. Customers do not need to change any settings - the DNS change should propagate automatically within the hour.

After the DNS change has propagated, customers should be able to send mail to email addresses that are hosted by Microsoft.

We’ll leave this incident open and will continue to monitor. (16:28 UTC — Jan 6)

Identified - We’ve still not heard from Microsoft but we believe we’ve identified the activity that triggered the block and are taking action to mitigate it at this time.

We’ll notify Microsoft of the actions we’re taking and continue to hold on for a response. (23:16 UTC — Jan 5)

Investigating - We’re still awaiting a response from Microsoft and have reached out to them as a reminder. (16:32 UTC — Jan 5)

On January 3 2022 at 20:47 UTC Microsoft began blocking mail sent from smtp.de.opalstack.com to domains that use the Microsoft 365 email system.

Microsoft’s own IP reputation and junk mail reporting systems indicate that there are no problems with smtp.de.opalstack.com so we’ve reached out to them for answers.

We’ll update this post as soon as more information is available.

In the interim as a possible workaround customers may create a new mailbox on our US mail server and use that temporarily for their outgoing email authentication. (21:40 UTC — Jan 3)

[Resolved] German SMTP blocked by Microsoft

Sat, 18 Dec 2021 19:30:00 +0000

Fixed - We’ve still not received confirmation from Microsoft that the block was lifted, but we’ve seen no further blocking activity since 23:50 UTC on 20 December 2021 so we consider this incident to be closed. (15:42 UTC — Dec 23)

Watching - Microsoft began accepting mail from smtp.de.opalstack.com as of 23:50 UTC on 20 December 2021.

We’re still awaiting official confirmation that the block has been lifted. (15:27 UTC — Dec 21)

On December 18 2021 at 19:30 UTC Microsoft began blocking mail sent from smtp.de.opalstack.com to domains that use the Microsoft 365 email system.

Microsoft’s own IP reputation and junk mail reporting systems indicate that there are no problems with smtp.de.opalstack.com so we’ve reached out to them for answers.

We’ll update this post as soon as more information is available.

In the interim as a possible workaround customers may create a new mailbox on our US mail server and use that temporarily for their outgoing email authentication. (19:30 UTC — Dec 18)

[Resolved] German SMTP server blocked

Mon, 08 Nov 2021 12:00:00 +0000

Fixed - The DE SMTP server is no longer blocked. (15:39 UTC — Nov 10)

Our German SMTP server smtp.de.opalstack.com is currently on a block list.

We’ve identified and corrected the cause of the block, and expect the block to be lifted by November 11 2021. (12:00 UTC — Nov 8)

[Resolved] German SMTP offline

Sat, 12 Jun 2021 10:45:00 +0000

Fixed - The certificate has been updated and SMTP is now working normally. We’re reviewing and revising our internal procedures to minimize the chance of this happening again in the future. (13:40 UTC — Jun 12)

German SMTP was offline due to a problem with the server certificate. (10:45 UTC — Jun 12)

[Resolved] German SMTP IP range on MS block list

Wed, 12 May 2021 23:02:00 +0000

Fixed - Microsoft is now accepting mail from smtp.de.opalstack.com. (19:44 UTC — May 14)

Identified - We’ve identified and corrected the cause of the block, and have passed our findings along to Microsoft with a request to delist the German SMTP address.

We’ll update this post when Microsoft have confirmed that the server is no longer on the block list. (17:51 UTC — May 13)

We’ve received some reports that outlook.com and other Microsoft mail services are blocking smtp.de.opalstack.com.

We’re investigating now and will follow up when we have more info. (23:02 UTC — May 12)

[Resolved] DE SMTP on Proofpoint blacklist

Fri, 12 Mar 2021 21:19:00 +0000

Fixed - The DE SMTP IP is no longer on the Proofpoint blacklist. (21:35 UTC — Mar 15)

Watching - We’re still waiting on Proofpoint to delist the DE SMTP IP address. (17:17 UTC — Mar 15)

One of the Opalstack DE SMTP IP addresses is currently on the Proofpoint blacklist. We’re working to have the IP de-listed and expect this to be complete within the next 24-48 hours. (21:19 UTC — Mar 12)

[Resolved] US SMTP server blacklisted by Microsoft

Fri, 24 Jan 2020 14:15:00 +0000

Fixed - We’ve verified that Microsoft is now accepting mail from the new US SMTP IP. (16:42 UTC — Apr 7)

Watching - The new US SMTP IP has been live for the past 12+ hours and we are seeing no problems with it.

Additionally, Microsoft has finally responded to state that the original US SMTP IP has been delisted.

We’ll continue to monitor until we’re satisfied that this is resolved. (17:03 UTC — Apr 6)

Identified - 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. (16:45 UTC — Apr 4)

Identified - 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. (21:28 UTC — Mar 16)

Watching - 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. (17:29 UTC — Mar 12)

Investigating - This issue is ongoing. We’ll continue to work towards resolution. (16:09 UTC — Feb 27)

Watching - Microsoft has once again assured us that our US SMTP has been removed from their blacklist. We’ll continue to monitor. (17:31 UTC — Feb 12)

Identified - 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. (15:13 UTC — Feb 6)

Watching - 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. (15:43 UTC — Jan 31)

Investigating - 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 (18:32 UTC — Jan 28)

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. (14:15 UTC — Jan 24)