Many of the security issues that lead to spam distribution occur in cyberspace. If an abuser has the ability to upload web pages without authorization on a web server, they can upload abusive content that they use to promote spam, but they can also upload, for example, a PHP script that acts as a mail cannon but is driven via HTTP commands. Sometimes malicious files are uploaded using FTP and passwords are leaked, which makes the problem similar to the one discussed in the previous paragraph. Again, maintaining good security for web applications and user passwords should help prevent this from happening. The real winner is to make it impossible for the web server to send mail directly, force all outgoing mail generated by the web application to use authentication through the SMTP wrapper, and write the relevant injection information to the mail header.
Monitor your logs!
Spend a small amount of time, or set up automation based on email volume and undelivered mail ratio, to monitor your mail servers. Quickly identifying problems and taking corrective action before an IP address or domain reputation starts to deteriorate can actually save you time and reduce the impact of incidents on normal mail flow.
Don't forget that spam sent via a web server will leave traces in the web server logs but not in the mail server logs, while spam sent by malware will usually bypass mail servers and leave no traces in any logs.
We believe that an internal mail server is still a viable solution for smaller organizations and should be the first choice when privacy/confidentiality issues are considered important. While it is true that a system administrator familiar with operating a mail system is necessary, the task should not be considered overwhelming once the above points are taken into account. All things considered, running your own mail server can be a very good investment.
The Registration Block List (RBL) is a public service that collects and catalogs information related to the "reputation" of domains and IP addresses, usually referring to the reputation of the sending email server (which it is not). Reputation is an overall ranking of how reliable that server (IP and domain) is for legitimate email, and in many cases how unreliable the server may be.
What is the purpose of RBL?
When you operate a mail server, you not only handle inbound mail from users, but also outbound mail sent by users. Due to the increasing technological demands on businesses to communicate online, there will always be those who choose convenience over security. This can happen when users decide to choose weak passwords over strong ones to simplify their daily workflow, but this has the adverse effect of creating vulnerabilities in the system.
In most cases, when the vulnerability is exploited, it generates spam that is sent from the server to other unsuspecting users on the Internet. When this happens, the server's reputation is recorded as a decrease on the RBL, and if it continues to happen, then the server's sending addresses are blacklisted.
What is the RBL blacklist?
The RBL itself is a service much like a phone book, with blacklists being marks against IP addresses and domains, indicating ig database that email originating from that address has been shown to be malicious and should not be trusted. If those recipient mail servers are checking the same RBL to verify the sending server, this may be reflected in emails sent to other servers.
Does this affect you?
Typically, shared hosting networks are protected by outbound spam filtering, which has been proven to reduce outbound spam originating from our network by 99%. While the vast majority of email sent from our network is legitimate, some clients may still send email that is marked as spam by mail filters or recipients outside of our network, resulting in the sending IP being blacklisted.