Outgoing email classified as spam

If you receive an Undeliverable email with an error that is similar to below example, it is probably because you don’t have SMTP authentication enabled. Your emails may have worked in the past, but they now fail with 550 errors.

Sample error:

“Your message did not reach some or all of the intended recipients.

Subject:    My email subject

Sent: 2016-05-16 04:32 PM

The following recipient(s) cannot be reached:

user@receiverdomain.com on 2016-05-16 04:32 PM

550 This message was classified as SPAM and may not be delivered”


Outlook 2010/2013

From the Menu Bar, Click the “File” tab.
Click the Info tab on the left and select “Accounts Settings”. Click “Account Settings”.
Select your Email account then Click “Change”.
Click “More settings”.
Select “Outgoing Server” tab.
Select the box beside “My outgoing server (SMTP) requires authentication”.
Select “Use same settings as my incoming email server”.
Click “Ok”.
Click “Next”.
Click “Finish”.


Mac Mail

From within Mac Mail Click Mail > Preferences > Accounts
Near the bottom of the window, look for “Outgoing Mail Server (SMTP)”, click the drop down arrow and select “Edit SMTP Server List…”
Click the “Advanced” button in the middle of the window and make sure Authentication is set to “Password”.
Click “OK” to close the edit window

Once you have added authentication, try re-sending the email that failed.