I've noticed that some emails will automatically open web pages upon opening the email. Unfortunately I cannot share an example email as it contains way too much personal information. This situation is not only annoying (I assure you it's extremely annoying), but is a security risk as well. An option to disable it should be added. I'm not HTML wizard, but it seems like this line in the header may be what's doing it. https://www.w3schools.com/tags/att_meta_http_equiv.asp
Is this as described in https://www.kde.org/info/security/advisory-20181128-1.txt? If so, it is fixed in KDE Applications 18.12.0.
Sure looks to be the same.
Thanks for the update; changing status. If you still see security issues, please add a comment or report directly to https://www.kde.org/info/security/