diff --git a/app/config.py b/app/config.py
index 9d08083e..d095380b 100644
--- a/app/config.py
+++ b/app/config.py
@@ -75,6 +75,16 @@ BOUNCE_PREFIX = os.environ.get("BOUNCE_PREFIX") or "bounce+"
 BOUNCE_SUFFIX = os.environ.get("BOUNCE_SUFFIX") or f"+@{EMAIL_DOMAIN}"
 BOUNCE_EMAIL = BOUNCE_PREFIX + "{}" + BOUNCE_SUFFIX
 
+# Used for VERP during reply phase. It's similar to BOUNCE_PREFIX.
+# It's needed when sending emails from custom domain to respect DMARC.
+# BOUNCE_PREFIX_FOR_REPLY_PHASE should never be used in any existing alias
+# and can't be used for creating a new alias on custom domain
+# Note BOUNCE_PREFIX_FOR_REPLY_PHASE doesn't have the trailing plus sign (+) as BOUNCE_PREFIX
+BOUNCE_PREFIX_FOR_REPLY_PHASE = (
+    os.environ.get("BOUNCE_PREFIX_FOR_REPLY_PHASE") or "bounce_reply"
+)
+
+
 # VERP for transactional email: mail_from set to BOUNCE_PREFIX + email_log.id + BOUNCE_SUFFIX
 TRANSACTIONAL_BOUNCE_PREFIX = (
     os.environ.get("TRANSACTIONAL_BOUNCE_PREFIX") or "transactional+"
diff --git a/example.env b/example.env
index a2d1963d..72c1adf7 100644
--- a/example.env
+++ b/example.env
@@ -44,6 +44,8 @@ SUPPORT_NAME=Son from SimpleLogin
 # prefix must end with + and suffix must start with +
 # BOUNCE_PREFIX = "bounces+"
 # BOUNCE_SUFFIX = "+@sl.local"
+# same as BOUNCE_PREFIX but used for reply phase. Note it doesn't have the plus sign (+) at the end.
+# BOUNCE_PREFIX_FOR_REPLY_PHASE = "bounce_reply"
 
 # to receive general stats.
 # ADMIN_EMAIL=admin@sl.local