Mac Mail problems

Hello my Macbook Pro running OSX 10.8.4 has recently refused to send emails from my SMTP account though I'm happily receiving emails on the corresponding POP account the settings all look to be correct and the accounts are working fine on my iPad. Has anyone got any ideas what I should try? It's crossed my mind that a spambot has installed itself and is preventing me using the account, I don't know how likely this is.

Many thanks, JeremyA

What message are you getting when you try to send mail?
Have you tried rebooting the Mac?
Double check your settings especially the out going server and port.
When all else fails delete the account and re-enter it.

Yep that did it - deleted account details then re-entered them. Many thanks for the prompt assistance.