In the past we have seen many guys whose hosting service was discontinued because of the spam. Most of folks did not send spam but their servers were shut down anyway bringing all their sites down and causing loss of potential revenue.

I will now try to explain why most of those disconnections took place.

As you know when spammers send spam they may specify any "reply to" address and "from" address they want and they can specify your email address or any emailaddress@yoursite.com.
Suppose you own domain.com domain name and it's pointed toward your server. There is one email box you have set up - mail@domain.com.

When a spammer sends spam and specifies mail@domain.com (your email address) as "from" address and people who receive spam report it, you will not have a trouble because headers of that emails will show that this spam was sent using some server other than yours, so it will be clear to spam fighting agencies that spam was sent not by you although your email address was specified as "from" address.

However, when a spammer sends spam and specifies, for example x@domain.com as either "from" or "reply to" address you might get in trouble.

What happens is this:
For example a spammer sends 100 emails and 10 of those 100 cannot be delivered because of the fallowing reasons:
2 email addresses are invalid.
and
8 email addresses are valid but their servers are down, or their boxes are over the quote at the time when the spam is being sent.
These 10 emails will bounce, and they will bounce to "reply to" address if it is specifies, if not "reply to" is specified, those 10 emails will bounce to "from" address.
So, those 10 email addresses will be bouncing toward x@domain.com.
Since there is no such a mail box as x@domain.com on your server, your server will bounce these 10 emails back.
2 of the emails that your server will bounce to the recipients they were addresses will not be delivered for the same reason they were not delivered the first time - those 2 email addresses are invalid. So, these 2 will be bouncing constantly between your server and other server(s).
8 of the emails will be delivered this time, because servers of owners of these email addresses are now up.
When these 8 emails will be delivered and those 8 recipients will report spam, you will get in trouble because the headers of those emails will show that they were sent from your server (when they bounced by your server).

It happens especially often when you have 2 or 3 letter domain names pointed to your server, because when spammers send spam they type whatever address in "from" or "reply to" fields, and it often looks like this gx@dkl.com.

To avoid this problem and to avoid mail problem (consider that instead of 100 emails, spammers sent as usually happens 1,000,000 emails, and instead of 2, 20,000 will be constantly bouncing between your server and other servers :lmao: ) you have to ask your host to set up mail so that all incoming email that is addressed to accounts that don't exist on your server gets deleted and NOT bounced.

There is no way this setting can be applied server wide, they will have to set this up for every domain name individually and some hosts will consider it as customization rather than troubleshooting and will charge you a fee for doing this job.
Also, some of hosts will be not aware of this and you will have to explain them what I have just explained to you. So you can avoid all the fees they would want to charge you by proving that this is troubleshooting, not customization. :D