In message <20010701013829.965587BB@starfruit.itojun.org>, Jun-ichiro itojun Ha
gino writes:
>
>	this is exactly the symptom with path MTU discovery problem
>	(though it seems that your provider's mail server uses a bit strange
>	TCP retransmission strategy i guess).  ask your provider to do either
>	of the following:
>	- turn off provider mailbox's path MTU discovery
>	- let ICMPv4 need fragment message through over some of the routers
>	  they have between DSL entrypoint and the provider mailbox

If you're using ppp(8), you can use the tcpmssfixup option.
-Angelos