said: 551 This mail server requires authentication before sending mail from

   a locally hosted domain. Please reconfigure your mail client to

   authenticate before sending mail. (in reply to MAIL FROM command)

Reporting-MTA: dns; smtp.mymailserver.com

X-Postfix-Queue-ID: 9CC261980F7

X-Postfix-Sender: rfc822; myusername@mydomain.com

Arrival-Date: Fri,  3 Jan 2014 09:26:27 +0200 (EET)

Final-Recipient: rfc822; x@x.com

Action: failed

Status: 5.0.0

Remote-MTA: dns; xhost.com

Diagnostic-Code: smtp; 551 This mail server requires authentication before

   sending mail from a locally hosted domain. Please reconfigure your mail

   client to authenticate before sending mail.

---------------------------------------------------error log---------------------------------------------------------

So, problem and solution is clear. I need to provide "My Outgoing Server needs SMTP Authentication" just as Windows based Outlook. But in Mac based Outlook there s no option for this. After Google research;

What i tried;

- Outlook>Tools>Accounts>More Options ; 

Authentication : User Name and Password Selected

User : *** Email address is removed for privacy ***

Password : Ok

Unqualified Domain : Left it Blank.

Nothing Changed. 

- Trying different ports 25, 587 exc. Nothing Changed. SMTP login failed also. Only works with 587.

- Trying to sent with SSL or without SSL on Outgoing Server. Nothing Changed. No difference.

- Trying to send mail 3 different clients. Apple Mail, Outlook 2011 and Mozilla Thunderbird. Nothing Changed.

- Trying to login with different username as; myusername or *** Email address is removed for privacy ***. Nothing Changed.

- Trying to send with free email clients like gmail, hotmail exc. It works! But we cant send email via these services to our customers of course.

I m run out of ideas, ma i find a bug or solution is still out there? Any ideas will be very welcomed.