diff --git a/data/templates/postfix/main.cf b/data/templates/postfix/main.cf
index cdf6aaf96..76d09c1cb 100644
--- a/data/templates/postfix/main.cf
+++ b/data/templates/postfix/main.cf
@@ -89,8 +89,11 @@ mailbox_size_limit = 0
 recipient_delimiter = +
 inet_interfaces = all
 
-#### Fit to the maximum message size to 30mb, more than allowed by GMail or Yahoo ####
-message_size_limit = 31457280
+#### Fit to the maximum message size to 25mb, more than allowed by GMail or Yahoo ####
+# /!\ This size is the size of the attachment in base64. 
+# Base64_SIZE = ORIGINAL_SIZE * 1,37 *1024*1024 + 980
+# See https://serverfault.com/questions/346895/postfix-mail-size-counting
+message_size_limit = 35914708
 
 # Virtual Domains Control
 virtual_mailbox_domains = ldap:/etc/postfix/ldap-domains.cf