[imp] can't login to pop3 server

[Boris Sagadin]

I'm trying to setup latest horde/imp on a new server, but login to my
POP3 server always fails. In logs, I get:

Sep 11 11:22:31 HORDE [error] [imp] FAILED LOGIN x.x.x.x to
127.0.0.1:110[pop3] as user10 [on line 287 of "/www/horde/imp/lib/IMP.php"]

I tried stracing POP3 server, and this is what I get:

[pid 31394] read(4, "CAPA\r\n", 4096)   = 6
[pid 31394] write(4, "+OK\r\n", 5)      = 5
[pid 31394] write(4, "TOP\r\n", 5)      = 5
[pid 31394] write(4, "USER\r\n", 6)     = 6
[pid 31394] write(4, "UIDL\r\n", 6)     = 6
[pid 31394] write(4, "STLS\r\n", 6)     = 6
[pid 31394] write(4, "EXPIRE NEVER\r\n", 14) = 14
[pid 31394] write(4, ".\r\n", 3)        = 3
[pid 31394] poll([{fd=4, events=POLLIN, revents=POLLIN}], 1, 600000) = 1
[pid 31394] read(4, "STLS\r\n", 4096)   = 6
[pid 31394] write(4, "+OK\r\n", 5)      = 5
[pid 31394] poll([{fd=4, events=POLLIN, revents=POLLIN}], 1, 600000) = 1
[pid 31394] read(4, "\26\3\1\0_\1\0\0[\3\1AB\303r\237\272\251\373%\202\10\321\212T\366\334p\247\353\274~\2\312\0057\22\215\27\v\254hC\0\0004\0009\0008\0005\0\26\0\23\0\n\0003\0002\0/\0f\0\5\0\4\0c\0b\0a\0\25\0\22\0\t\0e\0d\0`\0\24\0\21\0\10\0\6\0\3\1\0", 4096) = 100
[pid 31394] write(4, "-ERR Invalid command.\r\n", 23) = 23

Obviously IMP writes some junk(?) to a server after STLS command. Any
ideas why? How can I trace this further?

Regards,
Boris