Using IMAP works for me (pt.lu account)
The problem is, i don't want IMAP, I want POP. So it can only be a temporary solution.
Looking at connection doctor logs, it seems Mail asks for remote capabilities, then probably finds something it doesn't like there and quits...
CONNECTED Jul 24 16:38:57.932 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
READ Jul 24 16:38:57.992 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
+OK POP3 Ready ip-178-254-124-110.dyn.luxdsl.pt.lu 00023923
WROTE Jul 24 16:38:58.003 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
CAPA
READ Jul 24 16:38:58.029 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
+OK Capability list follows, mate
READ Jul 24 16:38:58.056 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
IMAP4rev1 LITERAL+ ID SASL-IR ACL RIGHTS=kxte QUOTA MAILBOX-REFERRALS NAMESPACE UIDPLUS NO_ATOMIC_RENAME UNSELECT CHILDREN MULTIAPPEND BINARY SORT SORT=MODSEQ THREAD=ORDEREDSUBJECT THREAD=REFERENCES ANNOTATEMORE CATENATE CONDSTORE SCAN IDLE LISTEXT LIST-SUBSCRIBED X-NETSCAPE URLAUTH
STLS
.
WROTE Jul 24 16:38:58.084 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
QUIT
READ Jul 24 16:38:58.109 [kCFStreamSocketSecurityLevelNone] -- host:pop.pt.lu -- port:110 -- socket:0x7fedf59744e0 -- thread:0x7fedf5178080
+OK QUIT