On Jul 20, 2010, at 8:09 AM, Hector Santos wrote:
It seem so random in what seems to be always accepting a transaction but
intermittently delivered or not.
Are you talking about the 4xx replies? If you check the text of the reply,
there's usually a URL with a bit more information about the reason. Same with
5xx, for that matter.
If you're saying the mail is just disappearing, it's possible that your users
have configured their accounts to delete suspected spam instead of putting it
in the spam folder.