Problems with the Recipient’s Email Server
Now we have some error messages related to bad configuration of the recipient’s email server. If you see a message similar to any of these, you must contact the recipient by other means (telephone, Facebook or any other form of contact) asking the recipient to contact the email server’s hosting company or the network administrator of the company (in the case of corporate emails) to fix the problem. Ideally, you should forward the error message to the recipient using a working email address, so he or she can forward to the person in charge of the email server’s configuration.
CNAME lookup failed temporarily. (#4.4.3)
Sorry, I wasn’t able to establish an SMTP connection. (#4.4.1)
If you get an error message that has something as:
THIS IS A WARNING MESSAGE ONLY YOU DO NOT NEED TO RESEND YOUR MESSAGE
This means that the recipient’s email server is facing a temporary issue, and your email server will keep trying to send the message (usually for the next four days). So, it is safe to simply ignore this error message. After this period (four days), if the message couldn’t be delivered, then your email server will generate a final error message, which you should analyze. Most likely, the problem will be at the recipient’s email server – as long as you didn’t mistype the recipient’s email address and the message ended up at the wrong server.
Of course, there are other error messages that you might see; we focused on the most common ones.