Linksys Router not allowing my e-mail to be sent

Hello everyone,

I recently purchased a wireless Linksys router (BEFW11S4) and PCMCIA
card network card combo and it has been working flawlessly… except for
my e-mail.

I actually have the router hooked up behind another router (some
obscure brand, GVC I think) in the house, since the house is heavily
wired with machines and it was easier just to have it as another point
off the main router instead of replacing it.

I did some research, and it seems that the reason my e-mail isn't
being sent is because of a packet fragmentation error is being caused
by the ICMP packet not getting back to my machine.

Well, I played around with some MTUs, and I got my mail partially
working, that is – small (very tiny, one sentence) e-mail messages
would be getting through just fine, but nothing bigger than that. My
MTU on my Windows machine is set to 1024, while my MTU on my Linksys
router is 1280. I don't know what the MTU on the first router is set
to, there doesn't seem to be an option in it's menu to change it.

Does anyone know how I can allow these packets to come through so I
can actually send some mail?

Thanks,
Mark