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how do you (A) send an email stating it's from someone else's (B) email, stating it is from B, with B's permission?
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how do you (A) send an email stating it's from someone else's (B) email, stating it is from B, with B's permission?
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To grant a user permissions to send on your behalf in Outlook:
To send as another user that has granted you permission:
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There are multiple possible ways. This can be done rather easily on any system that has a program called "telnet", unless some device blocks such connections. (For example, ISPs may prevent you from contacting remote mail servers. This is sometimes seen on "home"/"consumer" Internet connections.)
The number of computers that contain the "telnet" program is quite large, including a very large number of Unix systems, or systems running Windows 95 through Windows XP, and is addable on yet more systems including Windows Vista (and newer) and OS/2 3.0 (and quite possibly other versions too).
SMTP over Telnet shows the SMTP commands that can be typed in order to send a legitimate E-Mail message over the Internet. Anyone doing this needs to specify what E-Mail address the mail came from. In theory, they could type any E-Mail address.
In practice, some E-Mail servers will reject some E-Mail addresses, like E-Mail addresses that specify an organization that is known to use a different IP address than the IP address that is sending the E-Mail.
That has been a description that discusses some of the very technical description. Some different E-Mail programs will provide an easy-to-fill-out form, where a user can simply type whatever E-Mail address they want. For instance, E-Mail software called "pine" does not have such a field that can be filled out, unless the user goes through the list of options and changes the option that specifies whether such a field should be visibly provided. If the user wants to, then the user can type in another E-Mail address. The exact steps needed to accomplish such a task will vary based on which software people are using. (For instance, CConrad96's answer discusses information from a version of Microsoft Outlook.)
2Exchange/Outlook has a "send on behalf of" feature which lets you send emails as another user provided they grant you the previously mentioned permission. – CConard96 – 2016-05-11T22:15:38.873