diff --git a/.env.dist b/.env.dist
index 819bfe01..81ae68dd 100644
--- a/.env.dist
+++ b/.env.dist
@@ -101,6 +101,16 @@ ENABLE_POSTFIX_VIRTUAL_TRANSPORT=
 # etc.
 POSTFIX_DAGENT=
 
+# Set the mailbox size limit for all users. If set to zero, the size will be unlimited (default).
+#
+# empty => 0
+POSTFIX_MAILBOX_SIZE_LIMIT=
+
+# Set the message size limit for all users. If set to zero, the size will be unlimited (not recommended!)
+#
+# empty => 1048576 (10 MB)
+POSTFIX_MESSAGE_SIZE_LIMIT=
+
 # Enables a report being sent (created by pflogsumm) on a regular basis.
 # **0** => Report emails are disabled
 # 1 => Using POSTMASTER_ADDRESS as the recipient
diff --git a/README.md b/README.md
index 12996be6..729c35ec 100644
--- a/README.md
+++ b/README.md
@@ -190,6 +190,7 @@ services:
       - SASLAUTHD_LDAP_PASSWORD=admin
       - SASLAUTHD_LDAP_SEARCH_BASE=ou=people,dc=localhost,dc=localdomain
       - POSTMASTER_ADDRESS=postmaster@localhost.localdomain
+      - POSTFIX_MESSAGE_SIZE_LIMIT=100000000
     cap_add:
       - NET_ADMIN
       - SYS_PTRACE
@@ -303,6 +304,18 @@ Enabled by ENABLE_POSTFIX_VIRTUAL_TRANSPORT. Specify the final delivery of postf
 - `lmtp:<kopano-host>:2003` (use kopano as mailstore)
 - etc.
 
+##### POSTFIX\_MAILBOX\_SIZE\_LIMIT
+
+Set the mailbox size limit for all users. If set to zero, the size will be unlimited (default).
+
+- **empty** => 0 (no limit)
+
+##### POSTFIX\_MESSAGE\_SIZE\_LIMIT
+
+Set the message size limit for all users. If set to zero, the size will be unlimited (not recommended!)
+
+- **empty** => 1048576 (10 MB)
+
 ##### ENABLE_MANAGESIEVE
 
   - **empty** => Managesieve service disabled
diff --git a/docker-compose.yml.dist b/docker-compose.yml.dist
index 5a6f84f1..8768e57d 100644
--- a/docker-compose.yml.dist
+++ b/docker-compose.yml.dist
@@ -36,6 +36,8 @@ services:
     - VIRUSMAILS_DELETE_DELAY=${VIRUSMAILS_DELETE_DELAY}
     - ENABLE_POSTFIX_VIRTUAL_TRANSPORT=${ENABLE_POSTFIX_VIRTUAL_TRANSPORT}
     - POSTFIX_DAGENT=${POSTFIX_DAGENT}
+    - POSTFIX_MAILBOX_SIZE_LIMIT=${POSTFIX_MAILBOX_SIZE_LIMIT}
+    - POSTFIX_MESSAGE_SIZE_LIMIT=${POSTFIX_MESSAGE_SIZE_LIMIT}
     - ENABLE_SPAMASSASSIN=${ENABLE_SPAMASSASSIN}
     - SA_TAG=${SA_TAG}
     - SA_TAG2=${SA_TAG2}
diff --git a/target/start-mailserver.sh b/target/start-mailserver.sh
index e4b8d1df..2a610d68 100644
--- a/target/start-mailserver.sh
+++ b/target/start-mailserver.sh
@@ -19,6 +19,8 @@ DEFAULT_VARS["ENABLE_POSTGREY"]="${ENABLE_POSTGREY:="0"}"
 DEFAULT_VARS["POSTGREY_DELAY"]="${POSTGREY_DELAY:="300"}"
 DEFAULT_VARS["POSTGREY_MAX_AGE"]="${POSTGREY_MAX_AGE:="35"}"
 DEFAULT_VARS["POSTGREY_TEXT"]="${POSTGREY_TEXT:="Delayed by postgrey"}"
+DEFAULT_VARS["POSTFIX_MESSAGE_SIZE_LIMIT"]="${POSTFIX_MESSAGE_SIZE_LIMIT:="1048576"}"  # 10 MB by default
+DEFAULT_VARS["POSTFIX_MAILBOX_SIZE_LIMIT"]="${POSTFIX_MAILBOX_SIZE_LIMIT:="0"}"        # no limit by default
 DEFAULT_VARS["ENABLE_SASLAUTHD"]="${ENABLE_SASLAUTHD:="0"}"
 DEFAULT_VARS["SMTP_ONLY"]="${SMTP_ONLY:="0"}"
 DEFAULT_VARS["DMS_DEBUG"]="${DMS_DEBUG:="0"}"
@@ -123,6 +125,7 @@ function register_functions() {
 	_register_setup_function "_setup_postfix_vhost"
 	_register_setup_function "_setup_postfix_dhparam"
 	_register_setup_function "_setup_postfix_postscreen"
+	_register_setup_function "_setup_postfix_sizelimits"
 
   if [ "$SPOOF_PROTECTION" = 1  ]; then
 		_register_setup_function "_setup_spoof_protection"
@@ -653,6 +656,13 @@ function _setup_postfix_postscreen() {
 	       -e "s/postscreen_bare_newline_action = enforce/postscreen_bare_newline_action = $POSTSCREEN_ACTION/" /etc/postfix/main.cf
 }
 
+function _setup_postfix_sizelimits() {
+	notify 'inf' "Configuring postfix message size limit"
+	postconf -e "message_size_limit = ${DEFAULT_VARS["POSTFIX_MESSAGE_SIZE_LIMIT"]}"
+	notify 'inf' "Configuring postfix mailbox size limit"
+	postconf -e "mailbox_size_limit = ${DEFAULT_VARS["POSTFIX_MAILBOX_SIZE_LIMIT"]}"
+}
+
 function _setup_spoof_protection () {
 	notify 'inf' "Configuring Spoof Protection"
 	sed -i 's|smtpd_sender_restrictions =|smtpd_sender_restrictions = reject_authenticated_sender_login_mismatch,|' /etc/postfix/main.cf