openSuse leap 42.3 kmail 5.6.1 same problem with pop3, imap4, smtp protocol. when using account creation assistant you get not good security settings. once an account is created using "modify" and "automatically detect" you get good security settings. i joined captures for imp4 and smtp
Created attachment 108422 [details] imap settings with assistant
Created attachment 108423 [details] imap settings with "modify"
Created attachment 108424 [details] smtp settings in "advanced" tab with assitant
Created attachment 108425 [details] smtp settings in "advanced" tab with "modify"
Created attachment 108426 [details] smtp settings in "general" tab with assitant
Created attachment 108427 [details] smtp settings in "general" tab with "modify"
Problem still there. kmail 5.11.1