Fails how?

Fails because you get an arrore message you did not mention? Fails because it is not delivered. Despite Thunderbird telling you the message was send without any error message.

If it is the latter you will need to contact your mail provider and ask them what they are doing with your outgoing mail.

Thunderbird reports success when the providers server says all is Ok. So if it is not delivered after the server says Ok then you have to look to the next step in the chain of delivery.

Hi Matt,

Thanks for your reply :)

I am not getting any error message. I am receiving the email from the other person successfully, but other person cannot receive it.The configurations are all perfect. Even i tried with both IMAP and POP3, it fails still.

The final go is I can go back to my e-mail provider. Anyways, Thanks for Your help, Kindly help me if you get any more suggestions on this.

Thanks

So from your point of view: You get email from sender. you open it to read. you click on 'Reply'

Are the FROM and TO email addresses auto entered correctly? you complete the email and click on 'Send' button.

A copy is placed in your 'Sent folder - confirm ? you do not receive any message saying undelivered etc.

Do you have this issue with ant other email you send or is it only to that person ?

Do you get the same issue if you use 'Write' not 'Reply' and create a new message to the recipient?

Things you can check: make sure the email address is correct in your address book.

Ask the recipient to check their email client Junk and/or spam folder. Ask them to logon to their webmail account and see if the email has been auto placed in the 'Spam' folder.