Problems with mail sent to domain I'm having problems with email sending from php. If an email is sent to an email address with the same domain where script is, the smtp error 550 occurs: Requested action not taken: mailbox unavailable or not local . However, emails to all other domains go successfully. Those email addresses are configured on external domain control panel, not in Plesk, therefore server thinks that such mailboxes don't exist. Is there any simple and correct way to solve this problem and allow to send emails to not local mailboxes with the same domain? Currently, I have to disable mail service in the Plesk for the domain to allow sending emails.