Sendmail problem

Hi all,

Installed sendmail 8.14.1 on Fedora 6.
When I startup my email clients (Thunderbird) and try to send a mail I get the following error in my maillog on the server :

vvvlx01 sendmail[25287]: l9UBGgSX025287: [x.y.z.zz] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA


My mail client gets an error that the mail cannot be send. When I try to send it again, for one or another reason, the problem is gone, and the mail is send normally ... This situation repeats itself everytime I restart Thunderbird (same behaviour with OE!).

2 out of 3 computers have this problem, so on one computer everything goes well. So I compared several settings : Thunderbird settings are identical (except for username of course)

Any idea what's happening here?

Ok, didn't change anything, but now all 3 of my clients show the same behaviour. I would think isn't a server problem if it wasn't for the fact that all my clients react in the same way.
Anyone who has encountered the same problems? Please let me know !