Reading Time: < 1 minute For some reason Postfix sometimes get stuck.
To see if there are some email stuck in the queue you can simply type:
oktober# mailq
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
38A1BF3B1* 1152 Thu Feb 12 00:22:39 www-data@oktober.momeunier.fr
momeunier@gmail.com
-- 1 Kbytes in 1 Request.
Fortunately there is a little binary called postqueue that can help.