Serious problem with KMail

Hello list,

I hope someone can help me with this. I've recently created a new user for 
myself and recompiled the entire system from bare silicon on this Gentoo box 
to recover from a too-full /home partition that had been unnoticed for some 
time. (My ~/.local/share/sddm/xorg-session.log had grown to 15GB!)

Now when I come to set KMail up, nothing I can think of will make it collect 
mails from my local IMAP server.

I have three sources of mail:
  -	POP3 directly from my ISP;
  -	IMAP from my local server which fetches from my ISP via POP3;
  -	GMail.
I can retrieve POP3 messages, but they cause the usual problems so I don't 
want to use that source regularly - that's why I set up the local server in 
the first place. I can retrieve GMail messages with no problem, apart from 
having to go to the GMail web page to delete messages.

All outgoing mail should go via my ISP.

No matter how I set up the IMAP source, KMail seems to make no attempt to 
communicate with the server. I haven't brought out the tin-snips yet to 
analyse the IP traffic, but I've tried everything else I can think of. I've 
tried setting up the IMAP source first, with outgoing set either to the IMAP 
server or to my ISP's server. I've tried settting up the POP3 service first, 
then the IMAP - this is the order in which I defined them originally. I've 
tried setting up GMail first, second or third. I've even tried reverting the 
server to its previous version, which used to work with no problems.

So at the moment I have a write-only e-mail system (if this makes it out).

Can anyone shed a little light into my dark corner?

-- 
Regards,
Peter.

Gentoo stable
sys-kernel/gentoo-sources 4.14.65
QT 5.9.6, KDE frameworks 5.46.0, KDE plasma 5.12.5
KMail 18.04.3, akonadi 18.04.3
x11-drivers/xf86-video-amdgpu 18.0.1, dev-libs/amdgpu-pro-opencl 18.20.606296