"return;" existed before Apr 30, 2012(not inclusive). However, "return;" was erased in Apr 30, 2012. I think it is human error. "return;" is needed in POP3 protocol.
Merge pull request #4312 from colun/develop

POP3 protocol "return;" is needed after APOP request
Merge branch 'hotfix/4312' into develop

Close #4312