I'm having a ton of difficulty with with Mac Mail as well but not sure if the same as what is described in the problems here. Countless hours with Mac Help is getting me nowhere - wondering if someone can help here.
I don't seem to have trouble sending.
I'm on an imac and just upgraded from Tiger to Leopard. My mail ran fine on Tiger for about 3 months then started acting up. After an upgrade to Leopard, the problem continued.
I just continually get kicked of my mail account randomly. A pop up asking for the password appears. I type in and then am fine. Sometimes i can go for days with no problem, and then other days i need to do this 5x.
After hours with apple support, they had me do a complete erase and install of the OS. Things seemed fine for about 2 weeks and now the same thing is happening.
I originally had finger pointing between apple and my isp (Bell Sympatico in Canada). Escalated through Bell and they assure me in writing that nothing is wrong on their end - validated by hotmail running fine throughout these issues, 7 years with no problem when I was on PC, etc..
Ideas??? Thanks.