diff --git a/CHANGES b/CHANGES
index 8a374e1d9..26fe2018b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2549,3 +2549,5 @@
 * postgresql: fix issue when restoring large dumps
 * graphs: add cpu/disk/network usage
 * graphs: new disk usage UI
+* relay: add office 365
+
diff --git a/src/mail.js b/src/mail.js
index d5c699336..aec8156c4 100644
--- a/src/mail.js
+++ b/src/mail.js
@@ -682,7 +682,8 @@ async function createMailConfig(mailFqdn) {
         const enableRelay = relay.provider !== 'cloudron-smtp' && relay.provider !== 'noop',
             host = relay.host || '',
             port = relay.port || 25,
-            authType = relay.username ? 'plain' : '',
+            // office365 removed plain auth (https://support.microsoft.com/en-us/office/outlook-com-no-longer-supports-auth-plain-authentication-07f7d5e9-1697-465f-84d2-4513d4ff0145)
+            authType = relay.username ? (relay.provider === 'office365-legacy-smtp' ? 'login' : 'plain') : '',
             username = relay.username || '',
             password = relay.password || '',
             forceFromAddress = relay.forceFromAddress ? 'true' : 'false';