Error 450 4.7.25 Client host rejected, cannot find your hostname

[Ch3vr0n]

Recently i've needed to begin sending e-mails to an international client who seems to have a bit of a strict mailserver setup (as other mails sent from my VPS arrive in mailboxes just fine for other international contacts).

The exact error is in the subject Now i've done my preliminary research and this specific error seems to have something to do with the PTR record for the server. How do i fix this problem. There's currently 37 domains/hosting accounts connected to the VPS

 

[Active8]

PTR record must be done from your VPS provider or from his control panel , its not more than an reverse for your Ip adres e.g. 1.1.1.1 PTR srv1.mydomain.com be aware that your hostname must have also an A (and AAAA if ipv6) record in your DNS

 

[Richard G]

who seems to have a bit of a strict mailserver setup

You mean, you don't have a correct mailserver setup. Nothing strict about it, it's simple RFC's. I'm already wondering if you can deliver e-mail to hotmail or Gmail without a PTR/rDNS record and maybe you have some more not configured which should be configured.

Next to the fix that Active8 pointed out, you might want to visit mail-tester.com and send a test e-mail. Anything below a 10/10 score means you do not have your mailserver setup correctly.

 

[Ch3vr0n]

e-mail worked fine, still does. recipient received e-mails without attachment just fine, only with an attachment was there a problem. I could send mails just fine to hotmail, gmail or whatever provider, even my own ISP. That said, VPS provider first said "nothin we can do". Had to push them "you're in control of the IP, and VPS setup. Only you can change this" for a couple days. Suddenly it was possible lol, recipient then succesfully received a test mail with attachment. Go figure.

 

[Richard G]

I could send mails just fine to hotmail, gmail or whatever provider, even my own ISP.

So then you did have a correct PTR record present I presume? My reply was (as the one from Activ8) based on your own comment that the issue had something to do with the PTR record.

Had to push them "you're in control of the IP, and VPS setup.

LoL, and suddenly it worked again? Then they must have done something odd. In that case good you pushed them to fix it.

 

[Ch3vr0n]

I'm 100% sure the PTR record didn't exist. Used intodns.com to dig the dns records. The PTR was the only "warning" that was issued. Demanding they'd fix it at their VPS control was the only option. That said, i still find it odd though that the recipients mailserver accepted the simple text based mail perfectly with the MISSING PTR record. But the moment an attachment was added, the PTR was required or the mail got blocked.

 

[Richard G]

I'm 100% sure the PTR record didn't exist.

The you've been very very lucky that your mail was not refused yet by various systems including Microsoft mail. So yes I also find this odd that you did not have isseus before.
Because a PTR is a basic RFC requirement for good mail delivery. But if you've got one now... at least that part is good.

However, just to be sure I would visit mail-tester.com and send a mail like it says over there. I'm sure without PTR you never had a 10/10 score and anything below is asking for problems with mail, now or in the future.