Well what a fine how do ya do.
You've been blacklisted on the internet. Something slipped by security and a worm blasted it's way out. (And blast it did!)
You've isolated and cleared out the problem but now you have to deal with the mess.
The Blacklisting. The inability to send out e-mail because your public IP address is being rejected by every client.
So how can you confirm this?
A quick search of the internet on your choice of search engine will yield several results.
What do you need to know? You need to know the public Internet IP address your MX record, your mail server that is sending mail.
I found a very effective site www.mxtoolbox.com
Choose their tab "Blacklists" and type in the suspect DNS name or IP address.
If you're on the "HOTLIST" it will show up as a "RED" on their particular site (Other sites may show it up as "LISTED" or "BAD" or "MOST EVIL MAIL SERVER ON THE PLANET" (Haven't seen that particular one)
Most of the sites will have a hyperlink to the particular provider. Most of the particular providers will have a fairly easy method to remove your address from the list. (Some others bill and 'Express fee') to remove it immediately.
In some cases you will have clients that reject you simply based upon mail flow. TrustedSource.org is one such provider. They actually track the flow of email on the internet and web access and track 'Naughty sources'. Some clients subscribe to this particular type of service to determine who to reject mail from. Government of Ontario is one such place I have heard of using this service.
Dealing with trustedsource.org is not a pain either. A quick email to firstname.lastname@example.org with Domain and IP address details from a NON blacklisted email address will resolve the blacklisting from their system.
Take note, in most cases, the removal will take time. Your network goofed, it is YOUR problem and you cannot rush any of this.
So how do you avoid this from happening in the first place?
Yes obvious. Security. Keep your patches up to date, keep your antivirus and malware up to spec, make sure your firewall is as restrictive as possible to keep potential problems from flowing out.
And diligence above all, will keep you protected.
Remember, almost any problem can be solved. Just about every problem can be prevented.
The Energized Tech
Dedication and Inspiration creating the new Generation