[vchkpw] sending e-mail error

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Hello folks,   I’m having some odd problems with qmail+vpopmail in sending e-mails. I set everything correct in my mail client and I tried first to send e-mails to a mail account in my mail server and it worked just fine, I can log in and receive emails/attachments. When I try to send e-mails I get this error:  The message could not be sent because one of the recipients was rejected by the server. Server response: '533 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)'. (Account: 'mail.6s-gaming.com', SMTP Server: 'mail.6s-gaming.com', Error Number: 0x800ccc79). But the odd thing is that a minute later when the mail client tries to send the e-mail (it tries to send e-mails in the error queue) it simply goes just right and e-mail is sent. I tried for 5 minutes sending the e-mail and I kept getting that error over and over but when I idle the client and It tries to send it the mail is sent.     Thanks for all the help that comes! Rgs, Alex