Now that the move to Google Code is nearly 2 years ago, all SourceForge related stuff for HeidiSQL was removed today. That includes three mailing lists on which you probably were subscribed:
The first one was only used internally. The second and third one can be easily replaced by the update RSS feed at Google Code.
Hoping everyone is alright with this removal. This step should also help to decrease the large amount of emails we get every day.