blocked by my ISP's smtp server

[new]

Hello, 

I post on this newsgroup because I think my problem is in relation with dns. 

I have an ADSL connection with a french provider (wanadoo) with dynamic IP
and a network with a gateway with a e-smith server (SME 5.5) and I use a
DNS cache for my network on this SME box. I have domain with dynds.org. All
works fine, except a "little" problem. 

When I try to join the news.wanadoo.fr newsgroup server I can't join it,
when I try to send a mail with smtp.wanadoo.fr I have a message : 
 «<name at domain.tld>: Recipient address rejected: Relaying not allowed »,
when I send a mail with my qmail on the gateway no problem. 

I suppose the problem is my ISP see me like an "external user" when I try to
connect to news or smtp. 
I tried to change de db file of named with : 
IN      MX      5 myserver.mydomain.dynds.org
IN      MX      10 smtp.wanadoo.fr 

But I am very newbie with bind and this is, I supose, stupid. Anyway it does
not work.

I would like to know if this problem is realy linked to my DNS configuration
or if I am not on the good newsgroup ! If somebody can give me a direction
of research...

(forgive my bad english)

Regards