some users can't receive mails from domain.

[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 ?

thanks in advance
-- 
Selçuk YAZAR