Clients occasionally receive a mysterious message called something like "undeliverable mail" relating to mail that they have not sent.
This is not the same as receiving actual spam, which is dealt with elsewhere on the website.
Unless this is happening on a very regular basis (say 20 messages per day) there is no great cause for concern. What has happened is simply that a spammer has "harvested" your e-mail address (or a variant) and is using the address to hide the real origin. You may however want to learn more about the situation, so I have posted this article in response to requests from clients.
Here is a picture of the type of e-mail I am talking about. It is usually called a "bounce message"
A couple of things to note: the e-mail is addressed to the apparent sender. In this case the sender is claimed to be david10D@comfycomputing.net, but no such mail address exists. The spammers program is simply creating a number of apparent addresses at random in front of the @ sign and then adding it to the domain, in this case comfycomputing dot net, which it knows exists. This genuine suffix gives the spammer a big advantage over generating a random, probably non-existent domain such as skfyuijwu.com.
The spammers program will usually have a large library of genuine suffixes and churn through these systematically. This explains why these bounce messages seem to come in cycles.
Also you should note that the reason these bounce messages get through to non-existent mailboxes on your domain will be that the mailbox settings have been tweaked so that instead of just say firstname.lastname@example.org being an acceptable e-mail address, your mailbox has been set to accept anything in front of the @specimen.com. A lot of my clients like this option, it does mean that you have to put up with these type of annoying messages.
If you look at the specimen e-mail above, you will see that there are attachments. Whilst it is fairly unlikely that these contain viruses or Trojans, I have known this happen and so I would very strongly suggest that you do not open them.
If you need to discuss any aspect of this with me, please feel free.