I'm collecting emails at my website and I started one e-mail campaign using that list. The first welcome email I sent to 91 users returned 30 hard bounced, but the strange thing is that 29 are HOTMAIL addresses. Searching it on internet I saw other persons with same issue and a lot of different possible solutions. 

Can I assume this emails are really "bad mailboxes" or it could be an error? And if it could be an error , d o you know how to solve it? 

Thanks,

Marcus