Dynamic IP addresses are very often listed for exactly the reason you state, that spam has come from that address in the past, and because of this sending mail directly from a dynamic address is now actively discouraged. In fact, there are many blacklists that attempt to list all dynamic addresses on the assumption that it is much more likely that any email directly from them is spam. This has become even more common now that spammers are hijacking end-users’ computers to be their mail relay.
The standard has become that all email should be relayed through the ISP’s mail servers rather than local ones, or that if you must run a local outbound mail server you should get a static IP/subnet. Most ISPs now block outgoing mail from their dynamic IPs to any other mail servers than their own, so you might not even have the option of running a local outbound mail server on a dynamic IP address.
In general I’m a fan of the real-time blacklists (RBLs), but many mail administrators, even those that should know better, take too draconian an approach and deny all mail based on many different blacklists which all have different ideas of who should be listed. For small ISPs this can cause a lot of headaches when one problem user sends out some junk and gets the whole ISP blocked. Sure, its effective at getting that problem user promptly removed from the ISP, but at the cost of lost customers to the ISP who couldn’t send email while all the different lists take their time removing the blacklist entry. Most small ISPs who fall into this category would have removed the problem user anyway. Only blacklists with quick and painless ways of getting removed from the list should be used to deny email. All other blacklists should be used as only one of many criteria to filter spam from legitimate email.