diff --git a/src/calibre/gui2/email.py b/src/calibre/gui2/email.py
index b81f832336..5527226005 100644
--- a/src/calibre/gui2/email.py
+++ b/src/calibre/gui2/email.py
@@ -245,6 +245,10 @@ class SelectRecipients(QDialog):  # {{{
         if not to:
             return error_dialog(
                 self, _('Need address'), _('You must specify an address'), show=True)
+        from email.utils import parseaddr
+        if not parseaddr(to)[-1] or '@' not in to:
+            return error_dialog(
+                self, _('Invalid email address'), _('The address {} is invalid').format(to), show=True)
         formats = ','.join([x.strip().upper() for x in str(self.formats.text()).strip().split(',') if x.strip()])
         if not formats:
             return error_dialog(
diff --git a/src/calibre/gui2/preferences/emailp.py b/src/calibre/gui2/preferences/emailp.py
index dcc48af9e8..79c8492961 100644
--- a/src/calibre/gui2/preferences/emailp.py
+++ b/src/calibre/gui2/preferences/emailp.py
@@ -150,7 +150,7 @@ class EmailAccounts(QAbstractTableModel):  # {{{
             na = as_unicode(value or '')
             from email.utils import parseaddr
             addr = parseaddr(na)[-1]
-            if not addr:
+            if not addr or '@' not in na:
                 return False
             self.accounts[na] = self.accounts.pop(account)
             self.account_order[row] = na
diff --git a/src/calibre/gui2/wizard/send_email.py b/src/calibre/gui2/wizard/send_email.py
index ca9dae7d6f..8b43f52b9b 100644
--- a/src/calibre/gui2/wizard/send_email.py
+++ b/src/calibre/gui2/wizard/send_email.py
@@ -68,8 +68,9 @@ class TestEmail(QDialog):
 
     def run_test(self):
         from email.utils import parseaddr
-        addr = parseaddr(self.to.text().strip())[-1]
-        if not addr:
+        q = self.to.text().strip()
+        addr = parseaddr(q)[-1]
+        if not addr or '@' not in q:
             tb = f'{self.to.text().strip()} is not a valid email address'
         else:
             try: