I use earthlink/mindsprings smtp server to send the new user reg emails and haven't had one problem. Can't use sendmail because mindspring blocks port 25. haven't had any complaints like you describe. Only problem I have is people forget their password and don't seem to know what the lost password link is for and mail me to reset it for them. My only choice was to use mindsprings smtp server or change isps. Don't want to do the latter because I would be without broadband for a couple weeks during the changeover.
