Hi all,
What determines when your mail server is blacklisted on mxtoolbox.com? Do users or admins report your IP? Your ISP? Is there some kind of network scan that occurs?

There are several things that can get you listed as a SPAM relay on MXToolbox. One important thing to keep in mind is that MXToolbox queries several RBLs, it isn't in and of itself the blocking service, so you need to look at which ones are blocking you. One of the most common is running a mail server from a "residential" internet service. Often times residential accounts are assigned by a dynamic IP, which is pretty much an automatic flag, but even if they are static if they are still considered assigned from a residential block you will probably be flagged. Otherwise, IP addresses are usually blocked because of some form of reporting. I know that spamcop.net allows users to submit SPAM which becomes a statistical 'tick' with enough ticks causing you to be listed. Other systems have different methods and algorithms that they use, some of which are kept private so as to make it more difficult for spammers to get around them.

If you have been listed and you are not running from a residential service, you can try contacting the organization and ask to be delisted. They may also be able to tell you why you have been listed. If you have a problem with you system, such as a compromise of your web stack that causes you to send SPAM (btw, this does NOT require root level access) or operate an open relay and get re-listed it may become more difficult for you to get de-listed. MXToolbox should help by providing some good diagnostics regarding the status of your mail system.

As stated above there are many determining factors. One thing to keep in mind if you are using a business class IP address (usually static assigned to you by your ISP), and you are using it for outgoing mail only, be sure to contact your ISP to implement a PTR (aka reverse DNS) record resolving your IP to the domain you are sending for. If the MX record for your domain points to the incoming mail server (hosted elsewhere) , and you are sending out from a different IP address (other than the incoming), you want the reverse DNS record to point to the domain you are sending from. If you do not have this, the receiving party will notice and report that the forward and reverse paths do not have matching domains, thus flagging that domain or IP as potential spam.

I work at a telecom and deal with business customers every day who frequently get black listed because their sending mail server IP has no PTR/Reverse DNS record. (only in instances where they have a different incoming mail server hosted elsewhere)

Also, if you are mass mailing to multiple recipients, and they are clicking the "spam" button on their mail clients, it will flag your domain as "spam". If enough people click this, it is reported to blacklisting agencies who will ultimately black list you.

If you are already blacklisted, reach out to the blacklisting host and ask why you were blacklisted. That should lead you in the right direction. There are just too many factors that involve blacklisting to sum up every one.

Moved: This thread is more suitable in <NETWORKING> and has been moved accordingly to help your thread/question get the exposure it deserves.

Wow thanks for the replies, you guyz rock!