Sometimes correct isn’t good enough: Trouble sending email from Mac OS X Mail

So I’m troubleshooting a problem sending email in the OS X “Snow Leopard” Mail program.  The settings are correct: the SMTP server’s name is right, “Use default ports” is selected, SSL is turned off and Authentication is set to None.  However, every time I try to send the email I get an error “"Cannot send message using the server <server name>”.

I run the Connection Doctor with “Show Detail” selected and see references to ports 587 and 110 but no mention of the default outgoing message SMTP port 25.  Suspicious, I end up going back to Edit SMTP Server List and choose “Use custom port” and enter 25.  What do you know, the outgoing message goes through as happy as can be.

I tested this on another machine with the same problem and again sending worked properly after I set the custom port to 25.  Interestingly, it continued to work after I switched it back again to “Use default ports”.

This is the third particularly noteworthy time I’ve experienced a case where apparently correct settings simply fail to work.  On a Windows 2000 Server I was sharing a folder to the network and made sure the sharing and NTFS permissions were correct.  It just wouldn’t share.  I ended up resetting the share and NTFS permissions and then set them up again exactly the same way as I had originally but this time it worked like a charm.

More recently I was configuring port forwarding on a Linksys router for a Remote Desktop Connection.  The incoming port was correct and the workstation’s static IP address was right.  I could connect from the LAN but not through the router.  I ended up changing the IP address for an existing custom RDC port forward to direct it to the new machine (and set the listening port to match) and it worked perfectly.  Both forwards should have worked but only one did.

This is along the same lines as other situations I’ve experienced where some program option is correct but it’s not working.  Change the option to something wrong and then switch it back to the correct setting and it works.  What’s different?  Apparently nothing, but something changed “under the hood”.  The original setting had not registered properly but changing it and changing it back made the difference.

Sometimes computers aren’t logical, at least not at the user interface level.