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Doesn't that depend on my ISP running basically an open relay, if I'm trying to mail from me@hn.com and they only provide me@isp.net? Always figured they'd just

• kazinator 4y ago
  No because relays can be closed, and usually are. Your ISP's SMTP server requires authentication, using the credentials they gave you, and almost certainly uses TLS also. Your me@isp.net address (or perhaps the me part of it) is used for authenticating, along with the password. It will likely be used as your envelope address when sending; the SMTP command will be MAIL from: me@isp.net, though there could be flexibility there to accept other sending envelope identities. In any case, your mail's From: header will have the me@hn.com. If the ISP were to filter on the From: addresses after receiving the content of the e-mail, you'd have to negotiate something with them.
  • bongobingo1 4y ago
    > using the credentials they gave you, and almost certainly uses TLS also Ah yes, doh.