We got the same update and incidentally today we started getting even more reports of issues from Postmark... already sent the relevant details to Alex.
Scott On Friday, 07-08-2026 at 09:51 Brian Peterson via mailop wrote: Was there any update on this? The latest I got from PostMark Support was this: (From Friday the 31st 16:56 CST) " Here is a breakdown of what your firewall logs are telling us and why everything changed around late May: 1. The May 22nd Changes & Rejected Connections You are spot on that something changed in late May! Earlier this year, Postmark migrated our underlying outbound mailing infrastructure to a new system called KumoMTA, which is an open-source MTA built for high-volume sending environments. This new system is highly concurrent and attempts to connect and deliver messages much faster than our previous setup. The fact that the email succeeded on May 1st makes perfect sense, as it was sent before this upgrade was fully rolled out to those IPs." We've increased TLS connection limits on our end, but still no resolution. -Brian From: Alex Burch Sent: Thursday, July 30, 2026 11:18 AM To: Brian Peterson Cc: Scott Q. ; [email protected] Subject: Re: [mailop] Issues receiving from Postmark I am looking into this. I looks like we just have our TLS timeout set too strictly and we'll be expanding it today. Feel free to message me directly with any further issues or concerns regarding Postmark. Thanks, Alex -- Alexander Burch ActiveCampaign / Senior Deliverability Engineer mailto:[email protected] 1 North Dearborn St Suite 500, Chicago IL, 60602 On Wed, Jul 29, 2026 at 12:57 PM Brian Peterson via mailop wrote: We’re seeing PostMark issues as well (Started maybe June or May?). Two separate members of ours, using two separate app vendors, both of which seem to use Postmark. The only info I have third hand is “Timed Out waiting 5s for response to cmd=STARTTLS”. I can’t seem to find any indication of rejected connections from Postmark on my end. Firewall logging also shows all traffic flows allowed for the items that DO make it through. Did you ever make any progress on your issue? Might these be related? (May 22-24th also sticks out as to some sort of change made, but I’m not sure if that was the app vendor or PostMark themselves.) From: Scott Q. Sent: Wednesday, July 15, 2026 1:30 PM To: mailto:[email protected] Subject: [mailop] Issues receiving from Postmark If someone from Postmark is on the list..it seems we are having an issue receiving e-mails from you. Only error customers report is: smtp;400 KumoMTA internal: failed to connect to any candidate hosts: connect to http://65.39.216.37:25 and read initial banner: reading banner: Error Connection closed by peer reading response to cmd=NONE Sample e-mail: X-KumoRef: eyJfQF8iOiJcXF8vIiwicmVjaXBpZW50IjoiY2hyaXNAaW5zdXJldGhlYm9hdC5jb20ifQ== You can message me off-list - thank you! Scott _______________________________________________ mailop mailing list mailto:[email protected] https://list.mailop.org/listinfo/mailop _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
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