Unfortunately, however, all these tips are quite useless for your business address, so the only option is to try to dam the flood.

How can I block spam?
You can try to filter spam by having your email program look for tell-tale signs that a message isn't legitimate. However, spammers are prepared for this and have devised ways to trick filtering programs. Some data can easily be faked, such as a sender's name or sender's domain. Even the content of an email is easy to "fake." For example, senders of those ubiquitous Viagra adds dodge filters by using intentional misspelling, such as "V1agra" or "V-i-a-g-r-a." Another trick is to split the body of the email into a multi-part message so all parts need to be checked. If it's an HTML email, spammers could write "Vancouver Italy Atlanta Germany Russia Alabama," and only display the first letters by displaying the other characters in white text.

There are a lot of tricks, so it's not that easy to install a content filter. Instead I suggest you have a look at the offers from third party developers. Finally there are checks already in Lotus Domino R5 which could be enabled to check whether the connecting domain and/or the connecting hostname is listed in DNS (Domain Name Service). Unfortunately, if there is some mis-configuration, legitimate mail may be blocked. Additionally, you would have a big problem if, as recommended by Lotus, you have two Domino mail servers, one for incoming and one for outgoing mail. The server for outgoing mail need not be listed in the DNS, and therefore this email would be blocked.

Finally, the only thing that could hardly be faked is the IP Address of the sending server, which could be checked with blacklists.

What are blacklists?
There are dozens of different blacklists with different purposes. In general, they all have lists of IP Addresses. Some, like an RBL (Relay Blacklist), list all open Relay Addresses. Some others list all addresses which support spammers. Also their maintenance differs. Some are updated manually, some half-automatically, and some others are fully automated. If you want to get more detail on blacklists, feel free to check out some of them.

Even though blacklists are very helpful, they're not foolproof. It might happen that the sender of a legitimate email is listed in a blacklist. For example, if a service provider hosts different domains on one IP address and one of these users sent spam, it could blacklist everybody. So, blacklists can't detect 100% of spam messages, and the detected mail may not always be spam. Nevertheless, their quotes are very high, so they might help a lot.

How can I use these blacklists?
Lotus Domino 6 natively supports DNSBL (DNS Blacklists). If you're still on R5, you may use other add-ons from other vendors, or upgrade your SMTP-Server to R6. You only need to update the server for incoming SMTP email. All other Servers may stay on R5 if you like.

If you use blacklists, you have three different options for incoming messages: Log only, Log and Tag, or Reject. "Log only" will just display a message in the logfile of your server if an IP-Address is listed in a blacklist, but the mail itself is delivered normally without any changes. Thus, it makes no difference to the end user whether blacklists are used or not. "Log and Tag" will add a new item, $DNSBLSite, to the spam message. This item contains the name of the Blacklist where the IP Address was listed. And finally, "Reject" will not accept spam messages and reject it to the sender with a short message that you can configure.