I found the difference :
- backup mail (recived) :
Nov 27 01:33:11 ve-ara-23 postfix/smtp[2300353]: B634C100820: to=<reseaux-serveurs.dreal-ara@developpement-durable.gouv.fr>, relay=smtp.m2.e2.rie.gouv.fr[10.167.128.246]:25, delay=0.22, delays=0.04/0.03/0.07/0.07, dsn=2.0.0, status=sent (250...