[Users] "-ERR Authentication failed" while trying to access RuggedInbox account

[Mario Castelán Castro]

Hello.

I am trying to use Claws-Mail with a RuggedInbox account through POP3. I 
configured the account using the wizard. I enabled TLS and used the 
right password.

When trying to fetch mail, I get the error stated in the title of this 
message. Consulting the log, I get this:

-----BEGIN PASTED OUTPUT-----
* Account 'mariotest4 at mail.ruggedinbox.com': Connecting to POP3 server: 
mail.ruggedinbox.com:995...
[12:43:40] POP3< +OK Welcome to ruggedinbox.com
[12:43:40] POP3> USER mariotest4
[12:43:40] POP3< +OK
[12:43:40] POP3> PASS ********
[12:43:43] POP3< -ERR Authentication failed.
*** error occurred on authentication
*** Authentication failed.
-----END PASTED OUTPUT-----

I thought that the problem was that I made a mistake while entering my 
password. I checked more than 5 times than I was using the right 
password, and to be completely sure that I wasn't writing it wrong (as 
far as I can be sure of what my senses tell me), I made another account 
with a trivial password. Neither effort solved the problem nor altered 
the reported error.

I can access this account using Icedove, which is the Debian rebranded 
version of Thunderbird.

I am using the version of Claws Mail included in Debian 8, which is 3.11.1.

What is causing this problem and how can I fix or work around this?.

Regards and thanks in advance.