1 files changed, 1 insertions, 1 deletions
diff --git a/Lib/smtplib.py b/Lib/smtplib.py
index 399444a5cc..e10e327a82 100755
--- a/Lib/smtplib.py
+++ b/Lib/smtplib.py
@@ -668,7 +668,7 @@ class SMTP:
             self.rset()
             raise SMTPSenderRefused(code, resp, from_addr)
         senderrs={}
-        if isinstance(to_addrs, basestring):
+        if isinstance(to_addrs, str):
             to_addrs = [to_addrs]
         for each in to_addrs:
             (code,resp)=self.rcpt(each, rcpt_options)