Re: [exim] SMTP timeout sending mail to gmail

Quoting Avleen Vig:

> I don't think that should be the case.
> If Daniel is sending packets larger than 400 bytes, it is his OWN router
> that should complain that the packets are too large before they leave
> the network.

If Google/gmail is really blocking icmp fragmentation-needed (which I
doubt), it's the gmail server not receiving the icmp packet (telling it
that its packets are too big) and therefore breaking path MTU discovery.
I only wonder why the timeout is happening on outgoing mail, that would
indicate that the problem is on the Daniel's own mail server, but then
the issue would be with all outgoing mail.

Anyway, I wouldn't set the MTU to 400, it's a waste of bandwith and it
probably even violates RFC 791, which says the minimum supported
datagram size must 576 octets (with or without fragmentation, but with
PMTU all packets have the don't-fragment bit set).
A router with decent traffic shaping would be a much better thing.