Emailers! If you use 0845.com for re-direct - BEWARE!
If you use re-directs at all - check the blacklists first before using them - you may find your emails are going nowhere.
Also check your own domains regularly - (you never know!)
Here's the blacklist I checked - it's a free tool.
URIBL.COM - Realtime URI Blacklist
The domain above is not on ALL the blacklists out there - yet!