Hello - we host hundreds of customers on several servers and we've recently been experiencing problems with the outgoing email for our customers. Their mail is not getting through because our supposedly our hosting server was listed as "suspicious." We have jumped through all the hoops for the big ISP's and have searched all blacklists without finding any problems.

How can we get this problem solved? Any ideas?

Thanks!

You need to contact your datacenter. Is it only one particular ISP that's blocking you? Maybe AT&T ?

If you contact your datacenter, provide them the blocked email report, they can help get you unblocked. Most ISPs will only talk to the IP OWNER (the datacenter) and not the reseller (you).

Also, check your server and make sure that no spam was headed out.

Alas, that is one of my jobs here - sorting through blacklisted IPs and trying to get them straightened out. It's a real pain. Like Conor said, it could just be MSN or AOL or whatever.

You need to check if the mail server IP is blacklisted.
Check if there is reverse dns set for the IP.
Set spf records for the domains.
Setup domain-keys.

What is the main server IP? Most likely it has been blacklisted

Check your main server IP (by default the main IP is used as a mail server IP) in mxtoolbox . com and click "MX Lookup". Your IP will be checked against most of the RBLs and DNSBLs lists and will show you where the IP is black listed.

If you contact them they will provide you the exact reason of why you are listed in their database. You will have to make the changes accordingly and request them for the removal of your IP.

BTW, do you receive any specific error messages in the mail logs?

Quickly check your IP in black list RBLs and DNSBLs, contact your hosting/DC providers, more, check your rDNS add SPF record and check logs for client who is violating limitation rules , some client must be sending bulk email causing blacklist. Or you must have give space to spammer.

It seems your ip is blacklisted in real time blacklist. Use mxtoolbox to check your mail server IP address against 147 DNS based email blacklists. Exact link:http://www.mxtoolbox.com/blacklists.aspx . This issue may occur for one of the following reasons:
* Hosting account may be hacked and from there spammer/hacker relaying the mails to plenty of mail addresses as a real sender.
* Check mail server is set with reverse dns
* Check spf is set for all your domains. The SPF system is used to stop people from forging your domain name in email

All suggested very good info/task to do. We have faced such issue. Probably mail server ip gets blacklisted due to spamming. I have seen that there are few reseller creates new hosting accounts and use them to spam. Uploads the scripts and then delete that user/hosting account and gets script running.

Providing reliable email services can be a real challenge. We have found that email support makes up for a good portion of our day unfortunately.
Some of the biggest causes for this are as follows:
1. Email campaigns using outdated email lists.
2. Email accounts that have been compromised by spammers.
3. Uniformed email users and or undefined bulk email policies.
4. Hyper active RBL’s
Some Blacklists can be straight forward on the removal process while others are a real nightmare. What do the headers on the bounced email indicate? Email me one of the headers and or log information and I will see if I can make some suggestions.

Another fine example of why blacklists are bad.

I'm sure your outgoing mail server has just been blacklisted, make sure you contacting whoever and get it straightened out and add a spf record.

check the logs elaborately and check for the ip addresses, that if they are black listed. hope you will find something there.

Some blacklists, like SORBS are horrible. They blacklist you because there are no rDNS records set. What kind of crap is that? And then it's impossible to get that blacklisting removed for months at a time!

Try getting a different sub c from your provider, and check the outgoing logs for error messages which will tell you what RBL needs to be addressed,