diff --git a/DOCUMENTS/POSTFIX_CONF.txt b/DOCUMENTS/POSTFIX_CONF.txt
index f97a27fb..68b23c3e 100644
--- a/DOCUMENTS/POSTFIX_CONF.txt
+++ b/DOCUMENTS/POSTFIX_CONF.txt
@@ -59,6 +59,8 @@ hosts = localhost
 dbname = postfix
 query = SELECT goto FROM alias,alias_domain WHERE alias_domain.alias_domain = '%d' and alias.address = CONCAT('%u', '@', alias_domain.target_domain) AND alias.active = 1
 
+(Note: PostgreSQL does not have a concat() function, instead use e.g. .... alias.address = '%u' || '@' || alias_domain.target_domain AND ....)
+ 
 mysql_virtual_alias_domain_catchall_maps.cf:
 # handles catch-all settings of target-domain
 user = postfix
@@ -67,6 +69,8 @@ hosts = localhost
 dbname = postfix
 query  = SELECT goto FROM alias,alias_domain WHERE alias_domain.alias_domain = '%d' and alias.address = CONCAT('@', alias_domain.target_domain) AND alias.active = 1
 
+(See above note re Concat + PostgreSQL)
+
 mysql_virtual_domains_maps.cf:
 user = postfix
 password = password
@@ -86,6 +90,8 @@ dbname = postfix
 query           = SELECT CONCAT(domain,'/',maildir) FROM mailbox WHERE username='%s' AND active = '1'
 #expansion_limit = 100
 
+(See above note re Concat + PostgreSQL)
+
 mysql_virtual_alias_domain_mailbox_maps.cf:
 user = postfix
 password = password
@@ -93,6 +99,8 @@ hosts = localhost
 dbname = postfix
 query = SELECT CONCAT(domain,'/',maildir) FROM mailbox,alias_domain WHERE alias_domain.alias_domain = '%d' and mailbox.username = CONCAT('%u', '@', alias_domain.target_domain) AND mailbox.active = 1
 
+(See above note re Concat + PostgreSQL)
+
 # For quota support
 
 mysql-virtual-mailbox-limit-maps.cf: