Resolved 450 4.7.1 Client host rejected: cannot find your hostname

[strahinja]

Hello.

I am having a big issue with this.
I am using Plesk Onyx Version 17.5.3 Update #6 Web Host Edition on Ubuntu 14.04.5 LTS.

I get this error when users try to send mail to any adress @siol.net.

server postfix/smtp[5832]: F0994144279: to=<XXXX@siol.net>, relay=mailhub.siol.net[213.250.19.151]:25, delay=17223, delays=17223/0.01/0.27/0.06, dsn=4.7.1, status=deferred (host mailhub.siol.net[213.250.19.151] said: 450 4.7.1 Client host rejected: cannot find your hostname, [XXX.XXX.XXX.XXX] (in reply to RCPT TO command))

I researched and found out that the problem might be PTR record so I set that up and now from command dig -x of my ip adress i get that the PTR record is set at hostname of my server and the problem is still there.

Do you guys have any suggestion on how to fix this issue?

 

[AYamshanov]

Hi strahinja,

You need to have correct PTR-record visible anywhere from the Internet. Usually, this action can do only service provider (owner of network IP-range). In some cases, this is possible via service provider web-interface. You didn't post IP-address, so I can't check this but you can read how to check it here: Resolved - Plesk doesn't send Emails

 

[UFHH01]

Hi strahinja,

in addition to AYamshanov post, you could be interested in these links:

=> DNS Lookup for siol.net
=> Reverse DNS Lookup for 193.25.220.193​

As you can see, there is no reverse entry for your configured IP - address. Pls. contact your provider "Amis Telekom", if it is possible to set a reverse entry for static IPs to a FQDN and pls. note, that dynamic IP - addresses will not work, as they change often ( mostly every 24 hours ). ​

 

[strahinja]

I am sorry, maybe I have not explained my situation with more details.

I have static ip address for my server and I have set PTR record for it.
I can send and receive mail from all addresses except from domains that have MX mailhub.siol.net.
For example i have user@example1.com and it is hosted on my server. That address can send and receive mail from every other mail address except it can not send to anyone that has MX set as mailhub.siol.net, but it can receive from anyone with that same MX.

This is output that I get from my server:
telnet mailhub.siol.net 25
Trying 213.250.19.151...
Connected to mailhub.siol.net.
Escape character is '^]'.
220 mailhub.siol.net ESMTP server ready
EHLO server.maindomainofmyserver.com
250-mailhub.siol.net
250-PIPELINING
250-SIZE 68157440
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
MAIL FROM:user@example1.com
250 2.1.0 Ok
RCPT TO:xxxx@siol.net
450 4.7.1 Client host rejected: cannot find your hostname, [ipaddressofmyserver]

 

[AYamshanov]

Anyway, I think this is a variant of error about reverse DNS (PTR) Ok, maybe do you have correct PTR-record but mailhub.siol.net thinks differently about it?

Сan you check `nslookup IP-address` from mailhub.siol.net or see into logs on this mail server? Could you say IP-address of your server?

Additional link: Postfix Reverse DNS Lookup: 450 4.7.1 Client host rejected

 

[strahinja]

Anyway, I think this is a variant of error about reverse DNS (PTR) Ok, maybe do you have correct PTR-record but mailhub.siol.net thinks differently about it?

Сan you check `nslookup IP-address` from mailhub.siol.net or see into logs on this mail server? Could you say IP-address of your server?

Additional link: Postfix Reverse DNS Lookup: 450 4.7.1 Client host rejected

IP of my server is XXX (hidden after check)
mailhub.siol.net[213.250.19.151]:25

 

[AYamshanov]

Ok, PTR-record correct but mailhub.siol.net can't resolve IP-address to a hostname. You can delete ip-addresses from the post if you want to hide it.

I checked mailhub.siol.net with telnet from my router with IP-address 11.22.33.44 and PTR-record like 'l11-22-33-44.myProvider.org':

[root@gateway ~]# telnet mailhub.siol.net 25
Trying 213.250.19.151...
Connected to mailhub.siol.net.
Escape character is '^]'.
220 mailhub.siol.net ESMTP server ready
ehlo l11-22-33-44.myProvider.org
250-mailhub.siol.net
250-PIPELINING
250-SIZE 68157440
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
MAIL FROM:user@example1.com
250 2.1.0 Ok
RCPT TO:xxxx@siol.net
550 5.1.1 <xxxx@siol.net>: Recipient address rejected: siol.net

No any error like '450 4.7.1 Client host rejected: cannot find your hostname'.

 

[strahinja]

It started working.
It looks like the problem was old DNS cache at mailhub.siol.net.

Anyway, thank you very much for helping me.