It is not okay to leave the user with a mystic code that tells nothing about whose fault it was that the message could not be sent, which error exactly occurred, and, in particular, what can be done to resolve the problem. What if all a physician said was: "we have to do a hypopharyngoscopy"? You consult somebody who you think knows, a clinical dictionary or the web.
The most common SMTP error code when sending email is 550. Often, an email could not be delivered because it has been blocked as spam, either through an analysis of its contents or because the sender—or sender's network—is listed as a probably source of spam in a DNS blacklist.
Some mail servers check for links to malware as well and return an error 550.
Between January and August 2015, Optus used the expression “NBN-like speeds” in its advertising materials to describe the data transfer rates of its broadband service and specific broadband plans.
In the ACCC’s view, this term misrepresented that Optus’ speeds were comparable to speeds available on the NBN. The ACCC has a wide range of tools at its disposal to promote compliance with the ACL.
NBN's 2017 Corporate Plan subsequently revealed a significantly reduced HFC footprint; under the old plan, 34 percent of Australian premises were slated to receive an HFC connection, while 38 percent would be covered by Ftt N, fibre to the basement (Ftt B), or Ftt DP.
Under the new plan, however, this has been changed to between 43 and 54 percent being covered by Ftt N/B/DP, and between 21 to 27 percent by HFC.
In this case, the ACCC used two enforcement mechanisms – it issued infringement notices and accepted court enforceable undertakings.).
Under section 134A of the CCA, the ACCC may issue an infringement notice if it believes, on reasonable grounds, that a person has contravened certain provisions of the Australian Consumer Law (including section 29).
If the error message points to a specific blacklist or spam filter, do try to contact the list or filter administrator.