Thunderbird cannot send email saying 'unkown user' but sending via gmail succeeds

Question

I have set up a new email account on a vps,

I can download by pop3 the emails but if i send email to that account i receive the error 'unknown user' while if i send emails by a gmail account everything works.

any suggestion? is it a client or a server problem?

the vps is a centos web server with other working email accounts thunderbird is on windows 7

i try sending email other email accounts usually working without problems.

do you need other details?

Answer 1

I guess the server logs may give you the answer you're looking for.

Secondly you can test your email account using raw telnet like this:

telnet yourserver.com 25
hello clientname
mail from: [e-mail]
rcpt to: [e-mail]
data
Hello world
.
quit