diff --git a/README.md b/README.md
index 955a64c..b9315ab 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,17 @@ TLS and OpenDKIM support are optional.
 			-v /path/to/domainkeys:/etc/opendkim/domainkeys \
 			--name postfix -d catatnight/postfix
 	```
+	You may specify key selector if selector *mail* is already allocated by passing keyselector environment variable.
+	In this case $keyselector.private will be searched in /etc/opendkim/domainkeys inside container.
+
+	```bash
+	$ sudo docker run -p 25:25 \
+			-e maildomain=mail.example.com -e keyselector=app \
+      -e smtp_user=user:pwd \
+      -v /path/to/domainkeys:/etc/opendkim/domainkeys \
+			--name postfix -d catatnight/postfix
+	```
+
 3. Enable TLS(587): save your SSL certificates ```.key``` and ```.crt``` to  ```/path/to/certs```
 
 	```bash
diff --git a/assets/install.sh b/assets/install.sh
index 0b2aaff..bfd5e41 100755
--- a/assets/install.sh
+++ b/assets/install.sh
@@ -121,10 +121,10 @@ localhost
 *.$maildomain
 EOF
 cat >> /etc/opendkim/KeyTable <<EOF
-mail._domainkey.$maildomain $maildomain:mail:$(find /etc/opendkim/domainkeys -iname *.private)
+$keyselector._domainkey.$maildomain $maildomain:mail:$(find /etc/opendkim/domainkeys -iname $keyselector.private)
 EOF
 cat >> /etc/opendkim/SigningTable <<EOF
-*@$maildomain mail._domainkey.$maildomain
+*@$maildomain $keyselector._domainkey.$maildomain
 EOF
-chown opendkim:opendkim $(find /etc/opendkim/domainkeys -iname *.private)
-chmod 400 $(find /etc/opendkim/domainkeys -iname *.private)
\ No newline at end of file
+chown opendkim:opendkim $(find /etc/opendkim/domainkeys -iname $keyselector.private)
+chmod 400 $(find /etc/opendkim/domainkeys -iname $keyselector.private)