what is what it gets checked when sending an e-mail (blacklisted IP's)

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Hello,

I've got a notification from one of our customers which say that their mail server won't allow our e-mails to proceed into their system as we are on a blacklist.

I've seen that our public IP address is on some blacklists (4 or so) and I've started the procedure of removing our IP from there, but...

Which is the IP address that is being checked?

1. The domain provider public IP?

or

2. our public IP?

I mean, imagine that I'm sending one e-mail from a hotel in which they have got several problems due to different guests and that they have a blacklisted public IP address...
In that case, if option 2 would be used then probably our domain would become blocked due to other people.

Which is the way it works? do you know of any document out there that would explain this?

Thank you in advance. :thumbsup:

Posted 29-Apr-13 21:26pm

Joan M

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Manfred Rudolf Bihy · Accepted Answer · 2013-04-29T22:47:00

Solution 1

What gets checked is the IP adress of the SMTP server that is trying to deliver emails. What the denying side perceives as your SMTP servers IP adress depends on what network configuration you are using. Is it in a DMZ? Does the SMTP server have an IP adress directly reachable from the internet? etc. etc.

So the scenario you drew up really doesn't make much sense. If you are sending email from a hotel network (that has a blacklisted IP) this would only have an impact if you were using an SMTP server of the hotels network or had a SMTP server running on your laptop which is also unthinkable as that would afford configuration of the hotels network (routing) to forward packages designated to port 25 towards your machine.

Regards,

— Manfred

Posted 29-Apr-13 22:47pm

Manfred Rudolf Bihy

Comments

Joan M 30-Apr-13 4:54am

Thank you Manfred, I guessed that it was the right way to do it, but I was not sure of that. Thank you again!

Than having our external/public IP in some blacklists won't make a difference regarding the problems with our customers.

Manfred Rudolf Bihy 30-Apr-13 5:04am

You're welcome!

Still I consider having ones public IP in some blacklists is not a desirable thing and I'm also not sure what you mean by "the problems regarding our customers". Where exactly is your SMTP server located and under what IP is it seen from the outside? Besides that the customer already said they're blocking your emails because of the SMTP server being blacklisted or how else are your emails getting delivered to your customers SMTP server if not via yours?

I'm now more confused than before! :)
Can you shed some light on this?

Joan M 30-Apr-13 6:04am

Our public IP address is blacklisted in some lists :( (not a desirable thing I agree).
The mail server is outside our factory, in fact is in Madrid, based in the server farm the company which provides us the domain has.
If we have been blocked then, I understand that has nothing to do with our public ip address being blacklisted, it has relationship to our domain provider IP being blacklisted or (more probably) some viruses sent by someone in our company to the destination address...
I'm still waiting the real reason why our mails have been blocked, I hope they'll explain that to me soon.

Manfred Rudolf Bihy 30-Apr-13 6:21am

OK, I see and it all makes more sense now. Can you find out if you have a dedicated SMTP server (only for your company) or if it is a shared service that serves more than email domain? A shared email service may save you some money, but then email from other customers of your hosting service can spoil everyothers reputation as well, by using it for spamming or just sending virus contaminated emails.