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Oct 15, 2024 · If an email message that you send can't be delivered to the intended recipient, Microsoft 365 or Office 365 typically generates an error code and sends a delivery status notification (DSN) to you. This notice is also known as a "bounce message" or "bounce-back message."
Jan 15, 2021 · For receiving mail into Exchange: If the sending server does not support TLS, or if the TLS negotiation fails, Exchange Online will still accept messages unencrypted and without TLS (provided the sending server’s configuration allows that).
The message is rejected because the recipient’s mail server doesn’t accept the messages from the given sender. This happens when the sender’s email address or the domain or the IP address is on the custom recipient’s blocklist.
Jan 25, 2010 · SMTP codes can be so confusing, especially those SMTP response codes and SMTP error codes like the dreaded SMTP error 550. These are often returned in bounced email, such as “550 Requested action not taken: mailbox unavailable” or “550 5 2 1 mail from refused spam site.”.
Sep 19, 2024 · When you get a return email, the sending mail server (SMTP server) couldn't send your email correctly, or the recipient Mail server could not accept the email. The email will tell you: The email address that failed to receive the message. The specific reason for the failure.
Aug 29, 2011 · As usually, the answer is it depends. On the protocol level, as explained in the other answers, the delivery of email happens separately for each recipient, and failures should be reported for each recipient (though a mail server may choose to send a single failure message for multiple recipients).
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Oct 13, 2018 · If you try to send mail without proper authentication of your mail account, the mail server throws this error. Additionally, the authentication error also occurs when there is any mail server configuration issue – like domain not present in localdomains file or MX record mismatches.
