Selcuk Yazar:
> Hi,
> Some of our users can receive mail from national academic journal site but
> a few can't. when i look the logs, it says;
> ..
> timeout after END-OF-MESSAGE from rs248.mailgun.us[209.61.151.248]
> ..
> is it about our server or their server ?
Probably none of that, i.e. suspect a network-level problem. These
tend to be caused by middleboxes (firewalls, traffic shapers, etc.)
that break path MTU discovery, TCP window scaling, both, or something
else. As Victor suggests, only a packet sniffer can determine the
cause. No packet content is needed, but TCP metadata is essential
(handshake, flags, ack, window size, etc.).
Wietse
