I wrote a PHP5 program sending emails with PHPMailer. The problem is that when I try to send email from myn...@mydomain.com (I have such accound) I receive error:
  SMTP error: Invalid address: myn...@mydomain.com.
My domain is registered. A few weeks ago everything was working fine.
Could you tell me please what are possible reasons of this error?
Thanks in advance.

In comp.mail.misc,  <robert.magdziarz.2...@gmail.com> wrote:

There's nothing here that hints as to what the problem is. Some things
that could be going on:

        The mail system on the host that runs the PHP program
        is borked. Can you send mail from it using a different
        program? Even just a bare mail() from PHP would be a
        starting sanity check.

        The network the host that runs the PHP program is on is
        borked. Again can you send mail using a different program?

        There is something wrong with the destination; I checked
        mydomain.com and it seems to have a valid SMTP listener,
        but you probably lied about the email address.

        There is something else wrong, such as unprintable
        characters in the email address that you didn't cut and
        paste.

        Maybe it was even a transient error related to some
        temporary condition.

Elijah
------
mydomain.com.           86400   IN      MX      0 mx.mailix.net.

The only party who can give you an authoritative reason for this, or any  
other, error is the administrator of the mail server that rejected a message  
with the error. Any mail server is free to reject any email for any reason  
it wants. Although, in most cases, the reason for the rejection can be  
determined from the message, in cases where it's not, only the mail server  
that rejected a particular SMTP transaction will know why it did so.

application_pgp-signature_part < 1K Download

Eli the Bearded <*...@eli.users.panix.com> wrote:

Valid listener, but no such address (also assuming that the address
given by the OP is actually correct):

    $ host -t mx mydomain.com
    mydomain.com mail is handled by 0 mx.mailix.net.

    $ host mx.mailix.net
    mx.mailix.net has address 66.11.225.84
    Host mx.mailix.net not found: 3(NXDOMAIN)
    Host mx.mailix.net not found: 3(NXDOMAIN)

    $ nc -vvv 66.11.225.84 smtp
    Connection to 66.11.225.84 25 port [tcp/smtp] succeeded!
    220 mx.mailix.net ESMTP Exim 4.71 Wed, 12 Sep 2012 01:02:24 -0700
    HELO boo
    250 mx.mailix.net Hello boo [{your_ip_address}]
    MAIL FROM:<>
    250 OK
    RCPT TO:<myn...@mydomain.com>
    550 unrouteable address
    QUIT
    221 mx.mailix.net closing connection

Chris