XPost: alt.comp.software.thunderbird   
   From: nospam@needed.invalid   
      
   On Mon, 2/23/2026 7:46 AM, R.Wieser wrote:   
   > Mr. Man-wai Chang,   
   >   
   >> ISPs are trying to prevent non-business customers from running their own   
   >> SMTP server (TCP port 25) to spam the world.   
   >   
   > I'm not sure how blocking that port would block spamming, as using the   
   > equivalent SSL port for it would also work.   
   >   
   > AFAICT the usage of SSL connections has the same reason as always : snooping   
   > gets harder (for one, the users authentication cannot be sniffed anymore).   
   >   
   > Though I did hear, long ago, that some ISPs routed the SMTP port connections   
   > (standard and SSL) only to their own email servers.  For the reason you   
   > described.   
   >   
   > Regards,   
   > Rudy Wieser   
   >   
   >   
      
   The protocol is blocked by the ISP DPI box. It doesn't even matter   
   what port you attempt it on, Port 25 closes down just as easily   
   as Port 1025, if the SMTP protocol is sniffed by the DPI box   
   examining packet payloads.   
      
   At one time, network equipment designers would not look at a payload   
   for any reason. It was headers-only for analysis and transport. But   
   today, the DPI box examines whole packets and nothing is sacred :-)   
      
      Paul   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)