Source Address is not used in socket connection about aiosmtplib HOT 5 CLOSED

@rafaelrds ah, that's a good point. A better approach may be to use source_address after all then.

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Source address is a string sent to the SMTP server when connecting, identifying the client by IP or hostname (or any string, really). That's not very clear anywhere in the docs, but I don't think it's appropriate to use as local_addr.

To me the question is if I should add another param to set local_addr. I don't really understand the use case for that, I guess it's required in some network setups? What seems like it should work for that is to establish a socket connection and pass it (via the sock) param. Does that solve your problem?

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Yes @cole, it is for identifying the hostname and in our case, the sending machine can send e-mails for more than one domain, and has a few possible IPs when binding a socket. Let's say we are hosting from 1.2.3.4 but want to send from 1.2.3.5 if sending from domainA.com and 1.2.3.6 if it is from domainB.com (both are source addresses). I think adding a parameter to set local_addr might be the finest solution, so it can allow further customization. 🥇

Our current solution was to patch _create_connection method by creating a subclass of SMTP.
i.e.

class MySMTP(SMTP):
    async def _create_connection(self) -> SMTPResponse:
        ...
                else:
                    connect_coro = create_connection(
                        self.loop,
                        lambda: protocol,
                        host=self.hostname,
                        port=self.port,
                        ssl=tls_context,
                        ssl_handshake_timeout=ssl_handshake_timeout,
                        local_addr=(self._source_address, 0),
            )
        ...

As for the use case, some Email Service Providers defers messages when the client-ip field diverges from the IP presented at EHLO.

from aiosmtplib.

Hey @cole. I've noticed that the official CPython smtplib does use the source_address/hostname when creating a socket during connect() https://github.com/python/cpython/blob/master/Lib/smtplib.py#L339.

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Closed by #167

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