问题
Why does sending an email message from PowerShell with the Send-MailMessage command using the flag -Port 587 produce an error.
Command:
Send-Mailmessage -smtpServer mail.server.com -Port 587 -from "admin@domain.com" -to "user@domain.com" -subject "Test" -body "Test"
Error Message:
Send-Mailmessage : The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Must issue a STARTTLS command first
The PowerShell documentation says adding -UseSSL should specify that a STARTTLS command be sent, but even adding this flag may not resolve your issues.
Command:
Send-Mailmessage -smtpServer mail.server.com -Port 587 -UseSsl -from "admin@domain.com" -to "user@domain.com" -subject "Test" -body "Test"
Eror message:
Send-Mailmessage : Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
回答1:
Some SMTP servers may have been hardened to only accept TLS 1.2 for negotiating STARTTLS. In many cases Windows is configured to send TLS 1.0 by default when -UseSSL is specified.
To force Send-MailMessage to use TLS 1.2 it is necessary to add a line to the script before executing the Send-MailMessage:
Either enter:
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
or
[System.Net.ServicePointManager]::SecurityProtocol = 'TLS12'
来源：https://stackoverflow.com/questions/53785662/why-does-send-mailmessage-fail-to-send-using-starttls-over-port-587