Here's the technical reason why -> http://www.sendmail.org/tips/pathmtu.html
I have recently installed cable broadband through my ISP(American Communications). I am having difficulty in sending emails with attachements (either when I use Yahoo/Hotmail) or through my company's Lotus Notes email system (using my company's VPN). I have tried sending emails through multiple computers (laptop and desktop), but however, have not got any success in sending emails from any of them. I am connecting my computer directly through the cable modem and eliminated the role of my new router in this. I am using Motorola's cable modem SB5100.
I will appreciate any help.

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