diff --git a/conf/nginx.conf b/conf/nginx.conf
index 92b5de72..b8751bd5 100644
--- a/conf/nginx.conf
+++ b/conf/nginx.conf
@@ -52,7 +52,10 @@ server {
 		fastcgi_index index.php;
 		fastcgi_param SCRIPT_FILENAME /usr/local/lib/roundcubemail/$fastcgi_script_name;
 		fastcgi_pass php-fpm;
-		client_max_body_size 20M;
+
+		# Outgoing mail also goes through this endpoint, so increase the maximum
+		# file upload limit to match the corresponding Postfix limit.
+		client_max_body_size 128M;
 	}
 
 	# Z-Push (Microsoft Exchange ActiveSync)
@@ -62,6 +65,10 @@ server {
 		fastcgi_param PHP_VALUE "include_path=.:/usr/share/php:/usr/share/pear:/usr/share/awl/inc";
 		fastcgi_read_timeout 630;
 		fastcgi_pass php-fpm;
+
+		# Outgoing mail also goes through this endpoint, so increase the maximum
+		# file upload limit to match the corresponding Postfix limit.
+		client_max_body_size 128M;
 	}
 	location /autodiscover/autodiscover.xml {
 		include fastcgi_params;
diff --git a/setup/mail-postfix.sh b/setup/mail-postfix.sh
index 4c86b64a..9046952c 100755
--- a/setup/mail-postfix.sh
+++ b/setup/mail-postfix.sh
@@ -161,6 +161,7 @@ tools/editconf.py /etc/postfix/main.cf \
 	smtpd_recipient_restrictions=permit_sasl_authenticated,permit_mynetworks,"reject_rbl_client zen.spamhaus.org",reject_unlisted_recipient,"check_policy_service inet:127.0.0.1:10023"
 
 # Increase the message size limit from 10MB to 128MB.
+# The same limit is specified in nginx.conf for mail submitted via webmail and Z-Push.
 tools/editconf.py /etc/postfix/main.cf \
 	message_size_limit=134217728