Login fails if using explizit mode as the reader and writer remain the same after STLS command.
Take a look at https://issues.apache.org/jira/browse/NET-421 - it's nearly the same bug.
Bugfix for POP3SClient.java:
Therefore you have to change some variables in POP3.java from private to protected.
|Field||Original Value||New Value|
|Summary||Can't login to POP3S Server using explizit mode||Can't login to POP3S Server using explicit mode|
|Status||Open [ 1 ]||Resolved [ 5 ]|
|Fix Version/s||3.1 [ 12317744 ]|
|Resolution||Fixed [ 1 ]|
|Status||Resolved [ 5 ]||Closed [ 6 ]|