diff --git a/packages/isomorphic-core/src/imap-connection.es6 b/packages/isomorphic-core/src/imap-connection.es6
index 14189696b..d505f0a6d 100644
--- a/packages/isomorphic-core/src/imap-connection.es6
+++ b/packages/isomorphic-core/src/imap-connection.es6
@@ -346,7 +346,11 @@ class IMAPConnection extends EventEmitter {
         clearTimeout(socketTimeout)
         resolve(...args)
       }
-      return callback(cbResolve, reject)
+      const cbReject = (error) => {
+        clearTimeout(socketTimeout)
+        reject(convertImapError(error))
+      }
+      return callback(cbResolve, cbReject)
     })
     .finally(() => {
       if (this._imap) {
diff --git a/packages/isomorphic-core/src/imap-errors.js b/packages/isomorphic-core/src/imap-errors.js
index 63aefabe1..1222952e1 100644
--- a/packages/isomorphic-core/src/imap-errors.js
+++ b/packages/isomorphic-core/src/imap-errors.js
@@ -82,7 +82,7 @@ function convertImapError(imapError) {
     error.source = imapError.source
     return error
   }
-  if (imapError.message.includes('System Error')) {
+  if (/system error/i.test(imapError.message)) {
     // System Errors encountered in the wild so far have been retryable.
     error = new RetryableError(imapError)
     error.source = imapError.source