Hello Xavier

>The reason is that the message was bouncing:
>
>   ----- Transcript of session follows -----
>... while talking to fpo.mail.dk.:
><<< 421 fpo.mail.dk connection refused from [82.67.192.xx]
><xx @ post4.tele. xx>... Deferred: 421 fpo.mail.dk connection refused from
[82.67.192.xx]
>Warning: message still undelivered after 4 hours
>Will keep trying until message is 5 days old
>
>Any filters enabled on your side ?
My mailbox is handled by Denmark's largest ISP, and they have some filtering
enabled based on blacklists.

I have had trouble sending to my mailbox from another server the last week,
because the server was listed in the blacklist at:
	<http://cbl.abuseat.org>
because of missing or weak checking of HELO command in SMTP.

The error message was exactly the same in that case, as in your error message
above.

You could check your IP at <http://cbl.abuseat.org>

Regards
Helge Larsen