Looking for logging into the K9 Mail Gmail Secure site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the K9 Mail Gmail Secure site. After that you can login as usual with your login credentials.
https://k9mail.github.io/documentation/accounts/providerSettings.html
https://mobilsicher.de/kategorie/apps-appstores/k-9-mail-app-tipps-zur-problemloesung
https://github.com/k9mail/k-9/issues/3470
https://github.com/k9mail/k-9/issues/1460
https://github.com/k9mail/k-9/issues/655
https://github.com/k9mail/k-9/issues/2377
https://groups.google.com/d/topic/k-9-mail/03mERAWM22I
https://groups.google.com/d/topic/k-9-mail/69MojpiS6W8
https://productforums.google.com/forum/#!msg/google-mail-de/s5eE6BP6BXA/JXMbhY67BAAJ
https://www.kuketz-blog.de/mail-apps-zahlreiche-android-apps-uebermitteln-login-passwort/
https://www.reddit.com/r/privacytoolsIO/comments/5y0xkf/why_google_calls_k9_mail_app_less_secure_app_and/
https://android.stackexchange.com/questions/54559/how-do-i-setup-a-gmail-account-with-2-step-verification-in-k-9-mail
https://www.android-hilfe.de/forum/k9-k-mail-kaiten-mail.818/k9-einrichtung-mit-gmail-klappt-nicht.683680.html