Hi,
I started using Kmail again some time ago but now I am having big problems. I have 2 Gmail accounts, one is IMAP and the other is POP. I have 2 identities, one for each mailaccount and I have 2 sending accounts, one for each account.
Often the IMAP account can't synchronize the mailfolders, it just hangs there and after 5 minutes when it has to do it again, the percent-counter is changed to a lower value and nothing happens.
Receiving mail on the POP account normally works fine, it's seldom I have a problem with that one.

Sending mail from both accounts doesn't work. I get an error saying:
E-Mail Sending Failed
Failed to transport message. Connection timed out Failed
to store result in item. Item query returned empty result
set

I'm using Manjaro Linux 17.1.6 Hakoila - Testing, with Plasmashell 5.12.2, Kontact 5.7.2
When I search for my errors I get results from years ago, it seems this is an error which is present for a very long time.
Answers point to the fact that KMail is not accepted by Google as a safe E-mail client. I setup the Google 2-step verification but also that doesn't do it.
Authorization is not done right.
Added my comment to bug 390733. Hopefully something will be done soon about this cause this has been going on for many years already.

[EDIT] I have found messages on the Kubuntu forum from as early as January 2007, more than 11 years ago. This means for the last 11 years KMail does not play nice with GMail, or GMail does not play nice with KMail. Can the two parties please sit together and discuss the matter to solve this problem, which seems to be a problem for many people world-wide.

Situation with Akonadi / Kontact gets worse and worse.
I have 1 IMAP and 1 POP mail address, 1 calendar belonging to the POP address and an address book belonging to the POP address.
When opening Kontact synching mail takes forever, constantly I am watching a colored picture saying: retrieving folder contents.This counts for both the IMAP and the POP address.
I have used akonadictl fsck and vacuum to clean up the place but doesn't change anything.
In Akonadi console I saw that synching my address book was stuck at 14% so I uninstalled Kaddressbook and rebooted. No change.

In the POP-mailaddress (G-Mail) I get the same mails over and over, I can throw them away locally (when that works of course) but the next time I start Kontact they come back.

Am I the only one with these problems? Are there any people here on the forum who can help me? At the moment Kontact / Akonadi is useless.
I use Manjaro Linux, Testing branch (but also used the Stable branch - no difference)
KDE is at 5.12.2, Kontact 17.5.2
I just now downgraded Akonadi from 17.12.2 to 17.12.1, no change. Will try to lower it even more, hopefully find a version which works better.

Thank you.