You probably weren't using a custom service, it was just using the built-in local emailer. Like I said earlier, it is most likely spam filters which are catching your emails, as the local emailer has no trust factor.
I guess you are right.
What are you trying to accomplish?
Ans. I want customers should get verification email once they register on website after clicking on which they can post their topic.
What do you expect the Custom Service setting to do?
Ans : I got your point of custom service . If i use gmail service . Then how can i get my the credentials for a Gmail account in the respective fields