I have a problem in my e-mail . It seems that I have a virus.

How is that related? You may have a virus problem, but not necessarily a problem with your email.

My email send messages to different senders containing virus by itself.

How do you know that?

I would like you to scan my email.

Who do you mean with 'you'? If you really send messages with some sort of malware attached the damage is already done. The whole point of ant-virus software is to prevent that infected files get onto your computer in the first place.

if I changed my password, the website designer would know the new password or not .

What web site designer are you talking about? In any case, I'd hope for you that your provider will not store your password in the clear.

how can I change the password correctly

What password are you talking about?

Sorry , I didn't realized it is a forum . I found the message which shows that I am the " sender" in my mail box. I also received many messages with the title : " undelivered message " . I scanned my computer but the virus in the email itself.

I also received many messages with the title : " undelivered message " .

These kind of notifications usually give the exact reason why a message wasn't delivered to the recipient.

I scanned my computer

Good. What was the result?

but the virus in the email itself.

I've asked this before, but you didn't bother to respond to that question. Therefore again, how do you know that there is a 'virus' in messages you sent?

The problem is that : I didn't send this email to anyone . The email is sent by my account .

http://en.wikipedia.org/wiki/Backscatter_(email)