Securing the Exchange mail server

[AMISH]

I usually install mail servers to my clients. These customers generally have a fixed IP address. So they are blacklisted with the time when sending emails to the outside. Finally I use their ISP's SMTP relay as creating an SMTP connector in Exchange for example.

So the messages out to recipients and are no longer blacklisted.

Some time later I see they are again blacklisted and I am compelled to write to the guys who fight against spam, and I work with their ISP history that informs the "police" if I can afford to indicating that it was they who sold the IP and are not normal users but spammers.

Through a post I realized that the mail servers sending mail without the field are not allowed and these emails are considered spam.

My question is: what are the security measures that can be taken to properly protect mail server to avoid blacklisted, although we configure an SMTP relay?

[Big Fish]

Properly manage its DNS information, ie address records, mx and ptr. Configure a relay that is not an open relay. Monitor the traffic issued from inside the network. In these conditions nobody has a problem with its own blacklist domain and ip.

[AMISH]

Following your reply I would like to know if it is possible to configure the mail server so that it is not a relay host for spammers, for example, since SMTP is finally? So my ISP must see if his SMTP relay is not open if it is not safe.

I would like to know what settings must be created after creating the reverse zone as you spoke of PTR or is it sufficient to create the reverse zone?

To answer my question to configure its mail server so that it is not used as an SMTP relay, I think that if Exchange is installed behind a firewall, you can not use it to send mails I mean like SMTP relay not permitted if the source. Since in general do you must specify the SMTP server name type myserverexchange.domain.org level Relay SMTP settings.

The firewall should block all unauthorized traffic to the internal mail server in advance. But I also say as the SMTP port 25 is open, it should be enough for you using my mail server to send mail.

[Zachary]

Do not take it unkindly, but I think you're wrong to take such remarks. Simple common sense dictates to get a clear definition of 'open relay' or 'SMTP Relay' to google for example to understand the problem and solution.

Here nobody will teach you in detail. We request a minimum of professionalism. Some guys spend hours to write ebooks on the subject, just to start quickly and cleanly. Learn from there.

[Snake08]

An SMTP server behind a firewall may well be an "open relay"! Yes, because the firewall is only passes or rejects a particular traffic. But the "open relay" is a flaw in the SMTP protocol itself. It is very easy that test their server: simply enter the keywords. And we have the answer in a minute

I return to the beginning:

These customers generally have a fixed IP address. So they are blacklisted with the time when sending emails to the outside. Finally I use their ISP's SMTP relay as creating an SMTP connector in Exchange for example.

Common sense is obviously transfer mails to the ISP's SMTP and not try to submit oneself ... ip address with adsl (fixed).

I do not understand then that we could then be blacklisted. It would rather the ISP's SMTP server that would be.