Which is SMTP program you use, If you can give us a name we can try to find if there is any conflict or not?

The application is called Suunto. It only makes outbound connections to our mail server (read: send only, no receive).

What is the Suunto product name and version number? Is the client firewall set up to allow traffic for the Suunto product?

Sorry Suunto Fitness Solution 1.1.1.4. And why would the client firewall come into play when the application works fine if Internet Email Auto Protect is disabled? Does disabling Internet Email Auto Protect automatically remove block entries from the Symantec Client Firewall for SMTP, POP, and other types of mail traffic? While the firewall is installed, I have no policy configuration settings configured. 

Using Username/Password authentication over TSL/SSL?
In general settings, outgoing ports are configures to use port 25 (SMTP).
Do you have an exception to allow port 465 or 587?

I have seen other discussions where you need to configure one of these ports; 465 or 587- in order to get authentication to work.

Good point, something in the Internet Email Auto protect feature is seeing outgoing traffic as a threat.

Try disabling Outbound worm heuristics, and test if the issue goes away.

http://seer.entsupport.symantec.com/docs/331120.htm

Hi Khue,

Are there any entries created in the SEP Risk History, or any pop-ups on screen when the connection is blocked-?  SEP generally let sit be known when actions like this are taken. 

Thanks and best regards,

Mick

in SEPM go to Monitors-->logs-->risks and check any entry present related to this.If present add it ti centralized exceptions.

There aren't any popups or anything. I also see no logging for that specific device relating to blocked risks. 

I think it is better to open a case with symatec for this...