diff --git a/core/nginx/conf/nginx.conf b/core/nginx/conf/nginx.conf
index 7c831f1d..f9278f38 100644
--- a/core/nginx/conf/nginx.conf
+++ b/core/nginx/conf/nginx.conf
@@ -288,7 +288,7 @@ mail {
     {% endif %}
 
     # Advertise real capabilities of backends (postfix/dovecot)
-    smtp_capabilities PIPELINING SIZE {{ MESSAGE_SIZE_LIMIT }} ETRN ENHANCEDSTATUSCODES 8BITMIME DSN;
+    smtp_capabilities PIPELINING "SIZE {{ MESSAGE_SIZE_LIMIT }}" ETRN ENHANCEDSTATUSCODES 8BITMIME DSN;
     pop3_capabilities TOP UIDL RESP-CODES PIPELINING AUTH-RESP-CODE USER;
     imap_capabilities IMAP4 IMAP4rev1 UIDPLUS SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+;
 
diff --git a/towncrier/newsfragments/2485.bugfix b/towncrier/newsfragments/2485.bugfix
new file mode 100644
index 00000000..2e12fe89
--- /dev/null
+++ b/towncrier/newsfragments/2485.bugfix
@@ -0,0 +1 @@
+Quote SMTP SIZE to avoid splitting keyword and parameter in EHLO response