I have gone through the setup details many times.  My gmail account downloads email to my Outlook just fine, but when the Outlook outbox will not have success sending email through gmail.  
The port numbers are correct, POP3 - 995, SMTP - 465 with the boxes checked.  Outgoing server requiring authentication box is also checked.  
I check all the email addresses and passwords.  No luck.  
When I press send/receive in Outlook(not express) it downloads all the new mail but fails at sending.  Here is what it TELLS me:
"
Task '[email protected] - Sending and Receiving' reported error (0x8004210B) : 'The operation timed out waiting for a response from the sending (SMTP) server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP).'"

Any thoughts?  

I'm wondering if I shouldn't just bag Outlook and move to Thunderbird.  But I'm not sure if my PALM Treo can sync with Thunderbird.  Anybody know the answer to that?

Thansk so much.Thunderbird synch support is sketchy at BEST, I'm afraid.  Now there's something that would assist in breaking Outlook's stranglehold...  (Mind you, I'm a fan of Outlook.)

The most likely cause of this problem is attempting to send either to the wrong server or to the wrong port.  I don't want to INSULT your intelligence, but did you double-check the specified outgoing server for spelling mistakes, etc?  I just successfully connected to Gmail's SMTP server on port 465 as follows: [email protected]:~# telnet smtp.gmail.com 465
Trying 64.233.183.109...
Connected to gmail-smtp.l.google.com.
Escape character is '^]'.So the server is CLEARLY up and running.

Another possibility is that your firewall is blocking port 465 - have you checked that out?