Mails sent do not reach their destination. It appears in the Outlook sent as sent.

To check the exact reason - we have to follow few steps one by one as follows.

Due to following reasons mails may not reach their destinations,

Other End Problems
1. Email address typed is wrong or does not exist.
2. There is problem with the email address - like inbox capacity is full, incoming mail server is down.
3. Recipient received the email not in inbox rather in bulk/junk box - so tell him/her to check junk/bulk box.
4. Your email address is blocked by them (recipients).

Your End problem
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5. You have not clicked the option "Server Authentication" or other configuration problem you made.
6. There is virus problem in your computer creating malfunction for outgoing emails.
7. Your outgoing server problem.

So I am guiding how to check all points one by one tactfully to detect exact reason.

First verify the email address you typed - then you send email to the same email address from your different email.
Try to use same mail server (your end) for checking as some time few black listed mail servers are there.
You request the recipient to check the bulk/junk box - or send email waiting few hours.
Tell the recipient whether your email is blocked or the domain of your email address (as yahoo.com is domain of email [email protected]).

Now this is the very important point out of the all points - please consult with your mail server admin and check whether you have checked the Server Authentication Required option in mail client software like Outlook Express.
You please configure the same email in different computer (virus free) - try the same.
Wait few ours and send to other email addresses - and check.

I think you may easily rectify the problem.
Happy Computing.
I think I have been able to answer to solve the problem. Many Many thanks for using Fixya.