Hi all,
i'm currently using 1.23 since about two hours, but i had this problem
on 1.22 too.

I'm using a configuration like this:
WAN ---> rl1
LAN ---> VLAN2 on rl0
OPT1 ---> VLAN3 on rl0
OPT2 ---> VLAN4 on rl0

If i leave WAN MTU as default, i'm experiencing problem with some mail
server and some web sites ( http://m0n0.ch/wall too! ). Timeouts,
can't browse and so.
If i set WAN MTU to1496, it seems it is working correctly.(Without
modifying VLAN MTU).

I'm using DNS forwader, no captive portal and no proxyes, just NATting
connections.
I have my firewall connected directly with the router on WAN
interface, and i'm using a Netgear FS726 switch with tagged enabling.

Setting a lower MTU is the correct problem resolution, or perhaps i'll
have some problem with other websites in the future? Where can i find
a "technical" explaination about this problem (just for my interest,
to understand what's happening at low level;)) ?

Thank you i.a.
Marco