Sometimes, this type of things happens because of malware virus into the system or also by mistake deletion of dll files from the system so first scan your PC with malware scan or format C drive where all your programs files are saved.
That's strange - I am getting problems with my emails too. I have Thunderbird. I am receiving them all right but when I try to send them it is very reluctant. Keeps telling me there has been an error and that I should check with my provider etc. Then it wants to know if I want to send it later. No-o I want to send it right now. It does eventually send it but is very awkward about it.
I am exactly the same as Starbuckone. Haven't been able to send email for two days now except very occasionally, altho' still receiving them. I am with Virgin and Outlook Express. Virgin site does say it has a problem with broadband tho' but no other info. - rosy