stops emails

???what causes the firewall to block the sending of emails,will allow them in BUT not out,this happened about 2 weeks after loading onto the computer,worked 100% switched of for the night next time it was turned on no way could emails be recieved untill comodo firewall was removed.
nothing was changed , have reloaded the firewall programme again and it seems to be working OK at present,any suggestions would be appreciated operating XP PRO on an old IBM 40,like me a bit old.

The default settings would allow outgoing mail traffic.

That leaves either user interventions or influence of other security programs or left overs of those.