So out of the blue Mailcow appears to have stopped receiving any emails from external servers. If I send a test-mail I'm not getting any rejections messages either. Until just now where one user gives an undeliverable: > Your message to [recipient] couldn't be delivered. > > [user] wasn't found at [domain]. > info Office 365 nicky > Action Required Recipient > > > Unknown To address > > > How to Fix It > The address may be misspelled or may not exist. Try one or more of the following: > • Send the message again following these steps: In Outlook, open this non-delivery report (NDR) and choose Send Again from the Report ribbon. In Outlook on the web, select this NDR, then select the link "To send this message again, click here." Then delete and retype the entire recipient address. If prompted with an Auto-Complete List suggestion don't select it. After typing the complete address, click Send. > • Contact the recipient (by phone, for example) to check that the address exists and is correct. > • The recipient may have set up email forwarding to an incorrect address. Ask them to check that any forwarding they've set up is working correctly. > • Clear the recipient Auto-Complete List in Outlook or Outlook on the web by following the steps in this article: Fix email delivery issues for error code 5.1.10 in Office 365, and then send the message again. Retype the entire recipient address before selecting Send. > If the problem continues, forward this message to your email admin. If you're an email admin, refer to the More Info for Email Admins section below. > > > Was this helpful? Send feedback to Microsoft. > > ________________________________________ > > More Info for Email Admins > Status code: 550 5.1.10 > > This error occurs because the sender sent a message to an email address hosted by Office 365 but the address is incorrect or doesn't exist at the destination domain. The error is reported by the recipient domain's email server, but most often it must be fixed by the person who sent the message. If the steps in the How to Fix It section above don't fix the problem, and you're the email admin for the recipient, try one or more of the following: > > The email address exists and is correct - Confirm that the recipient address exists, is correct, and is accepting messages. > > Synchronize your directories - If you have a hybrid environment and are using directory synchronization make sure the recipient's email address is synced correctly in both Office 365 and in your on-premises directory. > > Errant forwarding rule - Check for forwarding rules that aren't behaving as expected. Forwarding can be set up by an admin via mail flow rules or mailbox forwarding address settings, or by the recipient via the Inbox Rules feature. > > Recipient has a valid license - Make sure the recipient has an Office 365 license assigned to them. The recipient's email admin can use the Office 365 admin center to assign a license (Users > Active Users > select the recipient > Assigned License > Edit). > > Mail flow settings and MX records are not correct - Misconfigured mail flow or MX record settings can cause this error. Check your Office 365 mail flow settings to make sure your domain and any mail flow connectors are set up correctly. Also, work with your domain registrar to make sure the MX records for your domain are configured correctly. > > For more information and additional tips to fix this issue, see Fix email delivery issues for error code 5.1.10 in Office 365. > > Original Message Details > Created Date: 28/10/2024 19:39:08 > Sender Address: > > Recipient Address: [recipient] > > Subject: Re: test > > > Error Details > Error: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient [recipient] not found by SMTP address lookup > Message rejected by: VI0PR09MB7389.eurprd09.prod.outlook.com > > > Notification Details > Sent by: VI0PR09MB7389.eurprd09.prod.outlook.com > > > Message Hops > HOP TIME (UTC) FROM TO WITH RELAY TIME > 1 28/10/2024 > 19:39:08 DBBPR09MB4858.eurprd09.prod.outlook.com DBBPR09MB4858.eurprd09.prod.outlook.com mapi * > 2 28/10/2024 > 19:39:09 DBBPR09MB4858.eurprd09.prod.outlook.com VI0PR09MB7389.eurprd09.prod.outlook.com Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) 1 sec > Original Message Headers > Authentication-Results: dkim=none (message not signed) > header.d=none;dmarc=none action=none header.from=[senddomain]; > Received: from DBBPR09MB4858.eurprd09.prod.outlook.com (2603:10a6:10:20c::19) > by VI0PR09MB7389.eurprd09.prod.outlook.com (2603:10a6:800:23c::15) with > Microsoft SMTP Server (version=TLS1_2, > cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8093.25; Mon, 28 Oct > 2024 19:39:09 +0000 > Received: from DBBPR09MB4858.eurprd09.prod.outlook.com > ([fe80::8526:26a7:5e14:30a4]) by DBBPR09MB4858.eurprd09.prod.outlook.com > ([fe80::8526:26a7:5e14:30a4%7]) with mapi id 15.20.8093.024; Mon, 28 Oct 2024 > 19:39:08 +0000 > Content-Type: application/ms-tnef; name="winmail.dat" > Content-Transfer-Encoding: binary > From: > To: NHendriks > Subject: Re: test > Thread-Topic: test > Thread-Index: AQHbKWvQiW/6/O5atUWKDW99EsfZ17KciYVR > Date: Mon, 28 Oct 2024 19:39:08 +0000 > Message-ID: > References: > In-Reply-To: > Accept-Language: en-NL, en-US > Content-Language: en-US > X-MS-Has-Attach: > X-MS-TNEF-Correlator: > msip_labels: > x-ms-traffictypediagnostic: > DBBPR09MB4858:EE_|AS2PR09MB6035:EE_|DBBPR09MB4858:EE_|VI0PR09MB7389:EE_ > authentication-results: dkim=none (message not signed) > header.d=none;dmarc=none action=none header.from=[domain]; > X-MS-Office365-Filtering-Correlation-Id: b4d11aed-9c59-4ca2-49ba-08dcf78830f5 > MIME-Version: 1.0 > X-MS-PublicTrafficType: Email > Return-Path: [sender] > X-MS-Office365-Filtering-Correlation-Id-Prvs: > 028c1dd4-39bd-42d8-66c3-08dcf7855365 I did change a config in the vars.inc.php to allow EAS. Changing it back does not help. I've restarted containers, restarted the VM and so forth. Running update.sh does some updates but it's not helping. Mailcow has been running for a view months now without any problems. Login via SoGo works fine, IMAP seems to be stuck at 'processing' when sending/receiving in Outlook as well and gives this error: > Task '[mailcow-user] - Sending' reported error (0x8004210B) : 'The operation timed out waiting for a response from the sending (SMTP) server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP).' I'm not sure which logs to look into. If anybody could help that would be amazing!

Yes, in fact all of the 4 domains point to Cloudflare: mail.[domain.tld] 104.21.27.95 So no idea if you are using Cloudflare as reverse proxy for your mailcow or not, but is it setup correctly? This we can't check, only that 104.21.27.95 doesn't respond to anything related to mail ```plain Nmap scan report for 104.21.27.95 Host is up (0.0092s latency). Not shown: 996 filtered tcp ports (no-response) PORT STATE SERVICE 80/tcp open http 443/tcp open https 8080/tcp open http-proxy 8443/tcp open https-alt ``` (**EDIT** by @"pkernstock"#1: Removed domains as per discussion author's request.)

Telnet the port remotely. Is it open? If not, is the service running? If the service is running, can you telnet it on the host machine? If you can telnet from the host machine and the service is running but you cannot telnet from a remote server, the ISP/Host is blocking the mail port.

The ISP isn't blocking anything as it's running in a datacenter. I can telnet in remotely.

@"NHendriks"#p19631 what port are you telnetting remotely?

Ports 25 and 587 both work. 465 gives a network error. [upl-image-preview url=https://community.mailcow.email/assets/files/2024-10-28/1730157044-795224-image.png]

Digged a little bit deeper and the only reason I'm getting the 'undeliverable' is because the domain was still added to my MS365 account. Not getting it on any other domains that I have removed before from MS365. So no emails are getting in but I can't seem to figure out why.

So the issue is resolved now that the domain is removed?

@"SimplyCorbett"#p19638 unfortunately it isn't. I have about five accounts and none of them are working unless it is internal, so if I use any of these accounts to send to any of these accounts. DNS is correct, PTR is set through ISP. All ports are open to the right VM and I have no idea where to look.

I guess the MX record for your domain is still pointing to MS365? Change it to point to your mailcow

@"DocFraggle"#p19649 I've checked all DNS records, everything is pointing to Mailcow. It has been working fine for about three months.

> @"NHendriks"#p19629 Error: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient [recipient] not found by SMTP address lookup > Message rejected by: **VI0PR09MB7389.eurprd09.prod.outlook.com** Are you sure? This indicates that the mail is sent to outlook.com, not your mailcow.

Mailcow stopped receiving since yesterday

pkernstock

@NHendriks Edited all posts with any mentioned domains.

NHendriks

Thank you very much! Also to the rest, thanks for guiding me into the right direction and helping me fix the problem!

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