Rdns issue

[Trustmeimadoctor]

Hi we are getting more and more emails getting rejected due to rdns issues

My problem is i just dont seem to he able to grasp what the solution is

Can anyone help?

Email path In

Is
Madeup.com
Mx=mimecast.com
Sends to protection.outlook.com
Then sends to a multi-tenent exchange environment

out
Same path except the mail server that sends it is not of the name madeup.com as its a hosted multi tenent environment

So what do i need to do?

[bitchstewie]

Difficult to be 100% sure without seeing some rejects/headers but it sounds as if you need to speak to the people who control the IP range your mail originates from.

Keep in mind there's a difference between a public IP of 1.2.3.4 resolving to "something.anything.valid" vs. mail servers that have been configured to reject mail from yourdomain.com where 1.2.3.4 doesn't resolve to something.yourdomain.com.

[sunbeam alpine]

Do you have SPF records defined in your domain DNS records?

[Trustmeimadoctor]

On this one yes the others are being put in next week

[sunbeam alpine]

Trustmeimadoctor said:

On this one yes the others are being put in next week

And have you tested them?

Tools here -

https://www.kitterman.com/spf/validate.html?

https://mxtoolbox.com/spf.aspx

[Trustmeimadoctor]

the spf is correct it has the ip of the mail server, mimecast and protection.office.com mxtoolbox has.it all green and ticked

[Trustmeimadoctor]

Isnt the issue

That the domain we are sending from is

Companya.com yet the ip it gets sent from resolved to
Smtp.hostingcompany.com

[Harpoon]

Can you post a redacted bounce message?

Is there RDNS setup for smtp.hostingcompany.com?

[Trustmeimadoctor]

Remote server returned 550 invalid rdns entry for (Ip of hostingcompany)

If do a ptr check on the ip it resolves to smtp.hostingcompany.com
If i click on smtp.hostingcompany.com it resolves to a different ip

[TonyRPH]

Why not just post the domain?

At least then some basic checks can be performed.

[WinstonWolf]

Trustmeimadoctor said:

Remote server returned 550 invalid rdns entry for (Ip of hostingcompany)

If do a ptr check on the ip it resolves to smtp.hostingcompany.com
If i click on smtp.hostingcompany.com it resolves to a different ip

You need to get your ISP to set a ptr record up that matches your static IP address.

[TonyRPH]

@Trustmeimadoctor

I sent you a PM.

[buggalugs]

I would cut out the hosting company SMTP outbound relay as it seems pointless, if anything use Mimecast outbound relay they will have all their DNS stuff sorted. Otherwise send direct your own IP, and make sure the forward and reverse dns matches, and ideally matches the ehlo name the server announces too.