XPost: comp.os.linux.misc   
   From: rich@example.invalid   
      
   In comp.os.linux.misc Lars Poulsen  wrote:   
   > On 2026-02-26, Rich  wrote:   
   >> In comp.os.linux.misc Lars Poulsen  wrote:   
   >>> On 2026-02-26, Lawrence D’Oliveiro  wrote:   
   >>>> On Thu, 26 Feb 2026 00:36:32 -0000 (UTC), Lars Poulsen wrote:   
   >>>>   
   >>>>> But when my Windows PC that sits on the same LAN tries to submit   
   >>>>> outgoing mail messages, they fail to go out. It appears that   
   >>>>> postfix considers them prohibited relaying, even though they are   
   >>>>> addressed to my own mailbox on my own local mail server.   
   >>>>   
   >>>>   
   >>>>   
   >>>> As a starting point, I assume you have “permit_mynetworks” listed in   
   >>>> your “smtpd_relay_restrictions”. In which case, make sure your   
   >>>> “mynetworks” sitting includes all the appropriate subnets for   
   >>>> relaying, and only those.   
   >>>>   
   >>>> You can use the “postconf -p” to display all current configuration   
   >>>> settings, whether explicit or defaulted.   
   >>>   
   >>> Thank you!!   
   >>> I think this may have solved this problem, so now I can get to   
   >>> see what the next blockage will be.   
   >>>   
   >>> As you know, "postconf -p" produces around 950 lines of output,   
   >>> so unless you know what to "grep" for, you are lost.   
   >>> I had read the hint in the comments in main.cf to look in   
   >>> manual section postconf(5), but it does not mention permit_mynetworks   
   >>>   
   >>> I am puzzled, as to why this is not set by default. I thought this was   
   >>> the reason why I was defining the list of mynetworks.   
   >>   
   >> mynetworks can't be "defaulted", because each site has a different   
   >> network layout.  And if it were "defaulted" then postfix with that   
   >> default would be an "open relay".  It (postfix) begins in "no relay"   
   >> state, and you have to explicitly enable allowing such from parts of   
   >> your network setup you want to allow.   
   >   
   > I was expecting that once I have set mynetworks, those networks would   
   > allowed to do relaying. Or that IF I need to explicitly set   
   > permit_mynetworks, there would be a note to that effect in the area   
   > where I set mynetworks. Instead, there is a note pointing to a man page   
   > that actually does not contain the needed information.   
      
   At least on the main.cf I have, there is info related to mynetworks_style   
   and mynetworks.  The big important one is:   
      
      # Alternatively, you can specify the mynetworks list by hand, in   
      # which case Postfix ignores the mynetworks_style setting.   
      
   So mynetworks overrides mynetworks_style if it is set.   
      
   But, how did you set mynetworks?  Did you specify a network address or   
   an IP address?  For it (mynetworks) to work right for a 'network' you   
   enter network addresses.  So if you use 10.0.0.0/24 as your network,   
   you'd put in 10.0.0.0/24 to allow any IP on that network to use the   
   server.   
      
   But if you put in just an ip: 10.0.0.1, then only 10.0.0.1 is allowed   
   to use the server.   
      
   > And would setting mynetworks to default to the set of networks that   
   > are directly attached to the host where postfix is running, be safe   
   > enough?   
      
   That depends upon what else is attached to that network.  If it is only   
   your local network, and only your machines, then yes.  If it has other   
   stuff (like a public wifi AP or something) then maybe not.   
      
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