Apart from making sure your mail is working please also ensure that it's not an account that can overflow it's Inbox, has server-side limitations, or goes off-line frequently (e.g. aol, googlemail, gmail, yahoo, hotmail etc)
So PLEASE use proper personal email addresses provided by your service provider, not freebies associated with spammers, hackers or those hosts prone to abusive mail practices
Also, PLEASE, do not use an eMail address where you set it to 'Out of Office auto-reply' !

(this bounces emails back to our server and then notifications back to Admins, creating additional work sifting 'bad' addresses and more important matters from someone simply away from their desk!)
gmail and tmail addresses are now not allowed -July 2009
Other dangerous and unreliable email hosts will likely be added to this list soon..
PS. Ultimately, members whose email addresses do not conform or whose addresses cause constant problems may be de-activated.