ASP Email Form: Sends To Some Email Addresses But Not Others..

here is the script i use:

Set myMail=server.CreateObject("CDO.Message")
myMail.Subject="subject"
myMail.From="me"
myMail.To=request.form("email")
myMail.TextBody="hello"
myMail.Send
set myMail=nothing

this script sends emails to some addresses but not others--and its based on the email service it's sending to. for instance, hotmail email addresses get the email, but mail.com email addresses dont get the email. i have tried sending it to other email hosts, too, and still, some work, some don't. what is going on here?