email with attachment does go to one user

1. Are you getting any delivery error messages?
2. Check the logs from your e-mail server.  If it is not your server, check with your ISP.
3. Check with the recipient if their mail domain uses a mail filter or Relay Block List of some type.
4. 1. If filter, ask them to check the filter and see if they can figure why your mail or mail server is being filtered.
   2. If Relay Block List, check the list to see if your mail server is listed.

- Tom
 

You could always make sure your domain is whitelisted on their end.

>> but when we send email with attachment to one email address which is an external email address,  he never get that email,  <<
Since user can get attachments via Hotmail, its likely that your domain name is blocked off  by the receiving mail server. Also get user to check if he has any policy activated for receiving mails.

As suggested by Tom check for error messages.

have you check if recipient is getting mail from you without attachment ?
if so then his inbound gateway is dropping your attachment by some rule or they have set incoming message size for your domain.

Yes,  with out attachment no problem,  he get all the email if there is no attachment,