Default mail app refuses to check my inbox and fails when trying to configure the folders

[mpxlbs]

Using hrev52713 x64 in UEFI mode.

I use One.com and have been for about 3-4 years now. Their server settings are:

imap v4
imap.one.com:ssl:993
send.one.com:ssl:465
Use Authentication: Yes
Use SSL/TLS/STARTTLS: Yes

Set up the e-mail application as follows.

Accounts
 MyEmail@MyDomain.CC
  Account name:  MyEmail@MyDomain.CC
  Real Name: MyRealName
  Return address:  MyEmail@MyDomain.CC

 Incoming
  Imap
   Mail server: imap.one.com
   Username:  MyEmail@MyDomain.CC
   Password: MyRandomGeneratedPassword
   Connection type: SSL
   [x] Remove mail from server when deleted
   [  ] Partially download messages larger than [ ]
   Destination: /boot/home/mail/in

 Outgoing
  SMTP server: send.one.com
  Username:  MyEmail@MyDomain.CC
  Password: SameAsIncoming
  Connection type: SSL
  Login type: ESMTP
  Destination: /boot/home/mail/out

Settings
 [X] Check every [5] minutes
 Show notifications [While sending and receiving.

No mails can be received. Mail folder configuration not downloaded.

Under incoming, I can select

Configure IMAP Folders

Doing so results in

Imap Folders
 Failed to fetch available storage
  Could not connect to server "imap.one.com:
  Invalid Argument.

Syslog does not show any relevant errors that I can see. Where would I look for them? Maybe you can see them.

[mpxlbs]

Syslog output file.

[humdinger]

You may find useful info by starting the mail_daemon from Terminal. As it's auto-restarted by the launch_daemon, you'll have to stop it first, before starting it from Terminal:

launch_roster stop x-vnd.Be-POST
/boot/system/servers/mail_daemon

Make sure the mail_daemon isn't still running after stopping the service by checking with ProcessController.