hostname in HELO wrong

[Wolfgang Breyha]

Hi!

R2mail sent an email to my servers using

Received: from eduroam-003-137.wlan.univie.ac.at ([77.80.3.137] helo=[IPv6:fe80::a0cb:fdff:fe7c:20ca])
	by justin.univie.ac.at with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256)

This HELO is wrong. It should be the PTR available in DNS and if there is none it should be the IPv4 literal if IPv4 is used.
The IPv6 link local address looks problematic. It's only a matter of IPv6 deployment and the first postmasters will block HELOs like this as [127.0.0.1] or localhost for IPv4.

Greetings, Wolfgang

[Wolfgang Breyha]

I just tested the full IPv6 case as well

Received: from [2001:62a:4:42d:xxxx:xxxx:xxxx:xxxx] (helo=[IPv6:fe80::a0cb:fdff:xxxx:xxxx])
	by joan.univie.ac.at with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256)

again the link local address is used as literal instead of the global address.

[Stefan Selbitschka]

Hi Wolfgang,

the usage of a correct address or hostname is not that simple in Android, since as developer you has no possibility to get the currently used network interface.

To determine the correct EHLO hostname I do the following:
- Iterate over all network interfaces
-> For each interface iterate over all addresses
--> Skip address if its a loopback address
--> If address is not loopback get hostname
--> If hostname is not equal to the hostaddress use it otherwise use the address enclosed in bracketts

The iteration stops for the first valid result and use this in the EHLO command.

This could lead to such problems, but I simply didn't found a better solution by now.

regards
stefan