I got the message in the heading after sending an email from a Yahoo account to the address of an institution that had always admitted my correspondence (until yesterday).
- What does the above error imply?
- What is 550?
- What is #5.1.0?
- What does [RCPT_TO] means?
- Would you recommend a web source where this coding is explained in a simple and understandable fashion?
- Which action should I undertake to get my mail message through?