[Users] too many bouces information message..

Already received some weeks ago this kind of message I just received today: " Your membership in the mailing list Users has been disabled due to excessive bounces The last bounce received from you was dated 08-Jan-2014. You will not get any more messages from this list until you re-enable your membership. You will receive 3 more reminders like this before your membership in the list is deleted. To re-enable your membership, you can simply respond to this message .. " At the mean time I just re-enabled my membership receiving confirmation message. What could be the reason? I'm only normally using via web my gmail account that I use for other mailing lists too, without any problem.... A difference is that I statistically find more messages from the list that gmails initally puts into spam and that I mark as "not spam".... Any hint here? Thanks, Gianluca