Can't send emails all of a sudden

My hard drive recently crashed on Mac Book Pro running Snow Leopard. Was finally able to reinstall everything and it was all working fine including mail (I was able to send and recieve). A few weeks prior Verizon had sent out a notice indicating email settings are changing. I changed them on my iMac, iPhone, iPad with no problems at all. This was a few weeks ago. Then last night I changed the settings on my Mac Book. Now I can't send out any mail on my Mac Book including mail that is not Verizon. I am able to recieve mail, but not send mail on my Mac Book. I was able to send mail prior to the setting changes. I am also able to send mail from iMac, iPhone, and iPad just fine. All the settigs are the same across all devices. Please help!