[MlMt] Mailmate using wrong network card

[Bill Cole]

On 19 Oct 2016, at 4:28, Fabian Blechschmidt wrote:

> Good morning everyone,
>
> I have the problem, that mail mate tries to use my virtual network 
> card, therefore having a wrong IP address when trying to access a mail 
> server, which blocks the connection (or the packet doesn't even reach 
> it)
>
> I have Parallels and VirtualBox installed. Both using a couple of IP 
> ranges to do their stuff. Neither of them is using 19.2.168.42.*
>
> My routing table - if I interpret that correctly, says, that 
> connections to 192.168.42.146 (which is the mail server), should rund 
> through default connection.

No, it says (in part) this:

> default            192.168.42.254     UGSc          777        0     
> en0
> 169.254            link#4             UCS             1        0     
> en0
> 192.168.42         link#4             UCS            30        0     
> en0
> 192.168.42.146/32  link#4             UCS             1        0     
> en0
> 192.168.42.254/32  link#4             UCS             2        0     
> en0
> 192.168.42.254     0:e:38:38:ed:ff    UHLWIir       778       92     
> en0   1196
> 192.168.42.255     link#4             UHLWbI          1      425     
> en0

Which, at first glance, suggests that 192.168.42.146 is an IP address 
assigned to your physical ethernet interface: a LOCAL address. However, 
for that I would expect to see a host route for that IP via lo0 with the 
flags "UHLWIi", which isn't present. Yet, the only other "UCS" route for 
a /32 net is for your default gateway, clearly a working device with a 
Cisco MAC address. I'm a bit confused as to what is going on here, but I 
don't think this can be a working config.

What address do you think your Ethernet interface should have?

> I understand, that with the domain "my.customer.ads" we don't know yet 
> which IP address the server has. I assume (but might be wrong here) 
> that we than simply use the default route and change the device if 
> needed after resolving the domain.

I am unable to parse that paragraph. I'm sure whatever you mean is 
important to your interpretation of this problem, but it does not makes 
sense in English.

Side issue: note that "my.customer.ads" has MX and A records in public 
DNS, but they are bogus. The .ads gTLD is a Google project and no real 
domains exist under it yet. I think you are using that name as a 
placeholder here, but maybe not.

> So in short: Whatever happens inside of MailMate leads to a wrong 
> network device to be used when contacting the server.

This is extraordinarily unlikely. It is technically possible for an 
application to specify what address and/or interface it uses for a 
specific connection, but for a client like MailMate there is absolutely 
no reason to do so. Normal client app behavior when setting up a TCP 
connection is to ask the OS to resolve a name to an IP address then ask 
the OS to open a connection to that IP address on a specific port. The 
OS typically determines the best local IP, ephemeral local port, and 
routing for a connection, NOT the app.

> Any idea what to do or how to debug? Tell me if I can help. I assume 
> I'm here until friday.

Fix your network config. If it does not seem wrong to you, the output of 
these two commands might help illuminate what's going on:

networksetup -getinfo Ethernet

ifconfig -av