![]() The link mentioned in the sTunnel message leads to the support article Enable or disable authenticated client SMTP submission (SMTP AUTH) in Exchange Online. The problem is that the original SMTP transmission method did not use authentication in 1982, and since the initial implementation, auxiliary solutions have been used to send e-mail securely. The abbreviation SMTP stands for Simple Mail Transfer Protocol, a protocol for sending e-mail, while POP3 and IMAP are used for retrieval. Let's see what this means, what Microsoft says about it and who is affected. But all other email programs that don't have that implemented requires POP3/IMAP and SMTP and can then get a problem. Outlook uses its own protocol for Office365 or Exchange Online. ![]() It is not trivial to implement it in your own programs. STunnel is a utility also for sending emails that transparently turns an unencrypted connection into a TLS connection. There came quite hints from MS, but I must admit that the consequences were not quite clear to me. The SMTP server did not accept Auth LOGIN PASSWD value. sTunnel reports: 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant. Today (at night) SMTP authentication was disabled for security reasons and you have to explicitly turn it on for the accounts you want. Robert wrote on July 13, 2022:Ī little chicanery from Microsoft. ![]() was kind enough to email me the information this morning (thanks for that), that there is a change in Exchange Online. ![]()
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