Subscribers E-mails

When testing the form I set up for subscriptions I noticed that if an e-mail address is close to one the is already subscribe smartlist doesn't subscribe it. I was just using short common names like bob@mydomain, tom@mydomain, etc. Then I used rob@mydomain and noticed that it wouldn't subscribe so then I tried rom@mydomain and som@mydomain and neither one of them would either. It seems that if only the first letter is different it won't subscribe. I'm just wondering if there is a fix for this or does everyone think that this won't happen too often anyways. Any thought would be appreciated. Thank-you, Ron