hosted email - ptr and smtp banners

We have found ourselves hosting email for a couple of different companies. I was not a planned thing, one company lost their building and equipment, we merged (sort of) with another company that wanted to retain their domain and a third company had their host go under.

All of a sudden we have four email domains coming into our network. It was all very temporary and now it looks like it may be permanent. Right now each domain has an MX record pointing to our firewall. The firewall forwards the request to our Barracuda 300 and then on to the appropriate mail server.

Right now only our domain has a proper ptr record. The other three are using our extra IP addresses. As well the Barracuda responds with an smtp banner that says

When we use the diagnostics tools at it has issues with the ptr record not matching and the smtp banner not matching.

I'm curious what would be the normal smtp banner to display in a hosting environment.

For the ptr records I can easily have them created as each domain is using a single IP address. If we continue to do this we will want to consolidate these onto one or two IP addresses, no need to use them all up. How do you deal with ptr records when more than one domain is using an ip address?

I'm guessing there should not be more than one ptr per IP address.

Do you create a single email domain like and change all the mx records to that? That gives just one ptr record and the barracuda should then sort the email by domain.

Thanks for any info
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Imtiaz HashamTechnical Director / IT ConsultantCommented:
SMTP Banner - Not the end of the world - leave it as your primary domain.

Don't do anything Catch All

PTR Record -> If it's to different IP addresses, you can assign a PTR record to each - however, again, as long as there is a correct PTR record to the primary domain, I wouldn't care.

The best practice scenarios wouldn't work in your case - but I wouldn't care that much :)
Simon Butler (Sembee)ConsultantCommented:
"When we use the diagnostics tools at it has issues with the ptr record not matching and the smtp banner not matching."

Ignore that test result. It has been wrong for years.
It is because mxtoolbox connects to your server as an inbound email message, then presumes that the outbound will be the same - it is not. Therefore the test is false reports. The FQDN you need to match the PTR is the one set on the Send Connector. The receive connector should be left as it is.

The PTR has no connection with the domain sending the email. All that remote servers are worried about is that the PTR has a matching A record that all resolve to the same place. There simply are not enough IP addresses out there for every domain to have its own IP.

When I build multiple domain sites I usually do one of two things.

1. Decide which domain is the primary, and have all DNS records set to use that domain. That includes MX records for the other domains. SRV records used for Autodiscover to point to the primary domain etc.

2. Register a generic domain and use that for everything instead, pretty much as option 1. This can often be the simplest solution if there are a lot of politics involved or people under brand A do not want to be associated with brand B.


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AJNSAuthor Commented:
Thanks for the info Simon.
Imtiaz HashamTechnical Director / IT ConsultantCommented:

How was my answer any different to Simon's?
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