Sisimai 5.0.1 has been released! The main changes are the implementation of the newly released SMTP error codes in Gmail and the bug fixes in the test code for the Perl version. Changes specific to the Perl version of Sisimai are indicated by Perl at the beginning of each item, and changes specific to the Ruby version of Sisimai are indicated by Ruby. And then, Sisimai 5 includes many changes that are not compatible with Version 4, so please check the Perl or Ruby version of your environment before installing or upgrading.