Resolved "Send from domain IP addresses and use domain names in SMTP greeting" does not work

[King555]

Plesk Onyx 17.5.3 Update 38
‪Debian 8.10‬ x64

I have my own root server with several domains and IPs. Each domain has it's own IP. Every domain has an MX record in the DNS settings (not in Plesk) which is again this domain (and not the main domain of my server).

To avoid that my mails could be seen as spam, I enabled this option in the mail server settings of Plesk:
"Send from domain IP addresses and use domain names in SMTP greeting"

I use Postfix as my mail server.

But obviously this option does not work (or I do not understand what it should do). I would think that by enabling this option, a connection to example.com:25 via telnet would give "example.com" as the greeting. But it doesn't. It gives the hostname of the server (i.e. the main domain).

Am I doing something wrong?

I do not want to publish my main domain as the MX record of all my domains, so I would like to use this option, if it really exists.

 

[Bitpalast]

The server is still running under the hostname. The difference in the SMTP greeting is only for mail that is mailed out from the server. When you connect to the server inbound the server responds with its hostname. When the server sends mail outbound, it can use different domain names in the greeting. This cannot be tested by connecting the the server through port 25. It can only be tested by outbound mail and an examination of the header of the mail once it is received by the recipient.

 

[King555]

OK, I think I understand. So when I send a mail from my account [email protected], my mail server connects to the target mailserver and says "Hello, I'm example.com", even if my hostname is NOT example.com, right?

I guess this means that in terms of anti-spam measures, it is OK that a connection to my server results in an SMTP greeting different from the receiving mail-domain's MX record.

I only ask because the site mxtoolbox.com says that my mail server isn't configured properly because of the SMTP banner (well, it also says that the banner contains an invalid hostname, but that cannot be true).

 

[Bitpalast]

Regarding the "invalid hostname", this could point to a missing or misconfigured PTR record in the data center routing. PTR is needed for reverse name resolution. The IP address is resolved back to the domain name (in this case the host name). If this does not work, recipients might think that the hostname is incorrect.

 

[King555]

The funny thing is that the PTR check on mxtoolbox.com reveals that the PTR record is absolutely correct, for IPv4 and IPv6.

Thank you, I will just ignore the test result.

 

[Sergio Manzi]

@King555: like you I used to use an external DNS, manually configured, as I didn't want to use my "web server" as nameserver too (on the rationale that keeping the two things separate would had helped me in case of troubles on the "web server"). I also lacked a second server to act as secondary.

Recently I discovered that my VPS provider (DigitalOcean) offers free DNS hosting and an extension exists for having Plesk to populate (via API) those DNS and keeping them in sync: satori, nirvana!

I'm telling you this because when I first saw a DNS zone created by Plesk I noticed a difference in the spf records compared to what I had always put ("v=spf1 a -all"): Plesk puts "v=spf1 +a +mx +a:myhost.mydomain.mytld -all". The important difference here is that also myhost.mydomain.mytld (the fully qualified name of my server, same as it appears in the PTR record) is cited in the spf record.

I think the above may help in some situation...

 

[AdrianC]

Even if it uses the correct HELO when sending, doesn't it mean it is a flaw if it cannot do that for incoming connections ?
If I have 2 dedicated IPss, I cannot seem to make it reply properly with different hosts in HELO message.

 

[Bitpalast]

That is because there is only one mail host, one mail server. You cannot masquerade that host name depending on the incoming connection, it is something that the mail server software simply cannot do, because it's a DNS thing.

 

[Sergio Manzi]

Actually with Postfix (if we are talking about Postfix...) there are ways to configure a multi-homed SMTP server to answer with different HELO/EHLO prompts depending on the incoming IP address. Have a look at this article or this one (the latter is probably overkill...).

Cheers,

Sergio