Telnet to Office 365

From command prompt
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telnet microsoft-com.mail.protection.outlook.com 25

ehlo yourdomain.com          "your Office domain address or domain.com"

mail from: youremail@yourdomain.com      your "Office365 Email address"

rcpt to: unknown@microsoft.com      "random microsoft address will work"

Please remember not to use Backspace in case if typed something wrong, hit enter and retype the whole command or wait till you received the output of the command.