Problem sending email to outlook.com

mickeypl

Hi,

I have a BGP over GRE tunnel and I have 6 public IP addresses assigned to this tunnel.
I checked these addresses on the blocking list and they are not blocked.
I have two email servers. One is MailCow (mail.domain2.co.uk-5.xxx.xxx.12) and the other is iRedMail (mail.domain2.co.uk-5.xxx.xxx.13)
RevDNS is set correctly for these two addresses.

The DNS entries are correct, at least I think so because when I send emails to gmail.com, the recipient receives them.
Below are the DNS entries:

;; SOA Record
domain1.co.uk	3600	IN	SOA	paige.ns.cloudflare.com. dns.cloudflare.com. 2048704812 10000 2400 604800 3600

;; NS Records
domain1.co.uk.	86400	IN	NS	paige.ns.cloudflare.com.
domain1.co.uk.	86400	IN	NS	watson.ns.cloudflare.com.

;; A Records
domain1.co.uk.	1	IN	A	5.xxx.xxx.12
mail.domain1.co.uk.	1	IN	A	5.xxx.xxx.12

;; CNAME Records
autoconfig.domain1.co.uk.	1	IN	CNAME	mail.domain1.co.uk.
autodiscover.domain1.co.uk.	1	IN	CNAME	mail.domain1.co.uk.

;; MX Records
domain1.co.uk.	1	IN	MX	10 mail.domain1.co.uk.

;; TXT Records
dkim._domainkey.domain1.co.uk.	1	IN	TXT	"v=DKIM1; p=DOMAIN_KEY"
_dmarc.domain1.co.uk.	1	IN	TXT	"v=DMARC1; p=quarantine; rua=mailto:postmaster@domain1.co.uk"
domain1.co.uk.	1	IN	TXT	"v=spf1 ip4:5.xxxl.xxx.12 ~all"

I have a problem with the outlook.com domain
When I send an email to my outlook.com account, I immediately get a message that the message could not be delivered.
Below is the content of this message:

This is the mail system at host mail.domain1.co.uk.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<user@outlook.com>: host
    outlook-com.olc.protection.outlook.com[52.101.10.4] said: 550 5.7.1
    Unfortunately, messages from [5.xxx.xxx.12] weren't sent. Please contact
    your Internet service provider since part of their network is on our block
    list (S3150). You can also refer your provider to
    http://mail.live.com/mail/troubleshooting.aspx#errors.
    [BN2PEPF000044A9.namprd04.prod.outlook.com 2024-01-27T09:10:26.366Z
    08DC1E0DE4084634] (in reply to MAIL FROM command)

As I wrote earlier, I also have an iRedmail server.
The DNS entries are identical for both servers, only there is a different domain, DKIM-KEY and different IP.
When I send an email to outlook.com with iRedMail, the emails are delivered to the recipient.

I also did a small test and replaced MailCow with the iRedMail server, of course I changed the DKIM entry to match iRedMail.
After sending an email to outlook.com, the recipient received the email.

I think there is a problem with the MailCow configuration.
After installing MailCow, I did not make any changes, I only added the domain and users.

As you can see, my DNS entries are different than what MailCow shows me in the configuration because when using the DNS entries that MailCow recommends, I was not receiving emails from outlook.com.

Can you help me with this problem?

If you need more information please let me know.

Thanks!

mlcwuser

mickeypl outlook-com.olc.protection.outlook.com[52.101.10.4] said: 550 5.7.1
Unfortunately, messages from [5.xxx.xxx.12] weren’t sent. Please contact
your Internet service provider since part of their network is on our block
list (S3150). You can also refer your provider to
http://mail.live.com/mail/troubleshooting.aspx#errors.
[BN2PEPF000044A9.namprd04.prod.outlook.com 2024-01-27T09:10:26.366Z
08DC1E0DE4084634] (in reply to MAIL FROM command)

The message seems pretty clear to me. MS is blocking the IP of your Mailcow server.

mickeypl I think there is a problem with the MailCow configuration.

I don’t think so. If you get blocked by Microsoft, it’s not necessarily because you’ve configured something wrong. In some cases they will simply block certain IP ranges or even individual IP addresses for no obvious reason. In many cases, it’s almost as if they do it by default when a new IP address starts sending email to them. Kind of like: You’re guilty until proven otherwise ;-)

mickeypl As I wrote earlier, I also have an iRedmail server.

Well obviously they’re not blocking the IP of the iRedMail server.

mickeypl

mlcwuser The message seems pretty clear to me. MS is blocking the IP of your Mailcow server.
I emailed them and they confirmed that this IP address is not blocked.

mlcwuser Well obviously they’re not blocking the IP of the iRedMail server.
I don’t think you fully understood.
I also did a small test…
When I change the IP of the iRedMail server-5.xxx.xxx.13 to the one used by MailCow-5.xxx.xxx.12 and send emails to outlook.com, the recipient will receive them without any problems. It doesn’t look like Microsoft is blocking this IP address.

mlcwuser

esackbauer I am not sending directly to outlook.com, I have a Sophos Firewall as MTA inbetween.

I regularly send to outlook.com directly from Mailcow from a VPS and never had this issue.

mickeypl When I change the IP of the iRedMail server-5.xxx.xxx.13 to the one used by MailCow-5.xxx.xxx.12 and send emails to outlook.com, the recipient will receive them without any problems. It doesn’t look like Microsoft is blocking this IP address.

Well, then I’m not sure what exactley is causing this, but this is certainly not a general issue with Mailcow, at least not in its default configuration, because as I said, I’m not experiencing this with my instance. What we do know though is that MS is blocking your messages for some reason, because the message you got was sent from outlook-com.olc.protection.outlook.com.

Maybe you could test your server with the following services, if you haven’t done so already:

https://dnschecker.org/
https://mxtoolbox.com/emailhealth
https://mxtoolbox.com/deliverability
https://www.mail-tester.com/

However, based on the information in your post and your cross-checks, everything seems to be fine on your end, and if Microsoft is the only provider you are experiencing email deliverability issues with, you probably have no choice but to contact them by using the link in the article @esackbauer posted.

esackbauer

https://docs.hetzner.com/robot/dedicated-server/troubleshooting/microsoft-blacklist/

The problem is not with mailcow I guess, because I can to any outlook.com user without problems.
But then again, I am not sending directly to outlook.com, I have a Sophos Firewall as MTA inbetween.

StvNbr

Hey, idk if you got it working or not, but i had the exact same issue. It took me a day for checking everything and i tried their delisting services for everything, but nothing worked. After some hours i sent an answer to their answer of the delisting request. After that they delisted me after a few hours and it was fixed. So just send them a mail and it should work again.

Good luck with it!

maddler

Microsoft tends to block messages coming from IPs with low or no past reputation.
Usually replying to their message and explaining that solves the issue.

Ballistic

I also experience this exact same problem to this day. Sometimes it resolves itsself in a few hours, sometimes never and I have to E-mail them. Only for it to work for a couple of days/weeks and then I get blocked again.

This is 100% a Microsoft issue in the Live/Hotmail environment. By now, I refuse to put any more time in it. It costs me 3 customers, 2 of those customers now also have experienced the problem at thier new hoster…

Hotmail/Live (Microsoft in my opinion) really needs to die.

ralfbergs

Check this out:
https://sendersupport.olc.protection.outlook.com/snds/
Here you can register with Microsoft to see your IP’s “sender reputation,” and you can also ask to remove it from their “blacklist.”