Email (server) settings opinion

Stratus_ss · Dec 14, 2015

Hi all,

Just wondering what your thoughts are on the following setting:

Code:

reject_unknown_client_hostname

I have been using it for the last couple of years on a server I administer and I haven't thought anything of it until today when an email started getting rejected. There is a travel agency that uses a third party for their email services. This caused their mail to be rejected because of the following:

Fictitious information below:

Code:

HostingCo has an IP of 6.6.4.3
TravelCo sends from travelco.com

Email originates from 6.6.4.3 but the reverse lookup does not match the email address of travelco.com. Email is rejected as being spoofed.

It had not occurred to me before that this sort of situation may happen. Do you think this reject setting is too strict in real life situations?

EarthDog · Dec 14, 2015

It an enterprise environment, it sure could be. In a small shop, that is IMO, manageable. You just need to keep an eye out on the logs/rejects.

don256us · Dec 14, 2015

I had a similar issue for an in-house email server for a small company. They used business class DSL from AT&T. I had to submit my MX info to AT&T and they added it to their DNS. That worked like a champ for me. I had to do it again when they upgraded.

petteyg359 · Dec 18, 2015

Stratus_ss said:
Hi all,

Just wondering what your thoughts are on the following setting:

Code:

reject_unknown_client_hostname

I have been using it for the last couple of years on a server I administer and I haven't thought anything of it until today when an email started getting rejected. There is a travel agency that uses a third party for their email services. This caused their mail to be rejected because of the following:

Fictitious information below:

Code:

HostingCo has an IP of 6.6.4.3 TravelCo sends from travelco.com

Email originates from 6.6.4.3 but the reverse lookup does not match the email address of travelco.com. Email is rejected as being spoofed.

It had not occurred to me before that this sort of situation may happen. Do you think this reject setting is too strict in real life situations?

There ought to be a TXT entry in DNS for travelco.com with an SPF entry defining 6.6.4.3 as an allowed sender, and your mail server should check the SPF record (last time I checked, exim did in most default configs, but you don't say what server you're using). I'd blame travelco.com for not properly setting up their end of SPF.

Stratus_ss · Dec 19, 2015

petteyg359 said:
There ought to be a TXT entry in DNS for travelco.com with an SPF entry defining 6.6.4.3 as an allowed sender, and your mail server should check the SPF record (last time I checked, exim did in most default configs, but you don't say what server you're using). I'd blame travelco.com for not properly setting up their end of SPF.

In the end I jumped through some hoops to contact the IT department and after about 6 hours of providing logs they got the email flowing. For the record I am using postfix back end.

I have TXT and SPF set up on my end, they were the ones that had the problem. To their credit they did take the time to work through it

Email (server) settings opinion

Stratus_ss

Overclockix Snake Charming Senior, Alt OS Content

EarthDog

Gulper Nozzle Co-Owner

don256us

Uber Folding Senior

petteyg359

Likes Popcorn

Stratus_ss

Overclockix Snake Charming Senior, Alt OS Content

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