One place that KMail does seem to have an advantage in security for accounts is that its security and privacy settings contain explicit warnings about HTML mail and email notifications within the settings window. If inexperienced users are setting up their own email, at least with KMail they are warned about some of the more obvious hazards.

KMail Account Configuration
Spread over half a dozen tabs, Evolution's account settings are unlikely to intimidate or confuse users. Yet this advantage seems small compared to some of KMail's features, including the separation of identifies from accounts, the customizing of templates for replying and forwarding messages, the list of supported character sets, and the enforcing of Outlook-compatible attachment names. Admittedly, users are unlikely to want these settings until they have some experience with KMail -- but, for those with well-defined preferences, KMail is more customizable than Evolution.

Evolution Account Configuration
Verdict: KMail, because it has more to offer more discerning and advanced users.
KMail uses Kontact's address books, which are well-integrated into the KDE desktop. By contrast, Evolution's are designed primarily for its own internal use and less integrated into GNOME, although some applications such as OpenOffice.org can use them as a data source.
Evolution's contacts are listed as address cards or as a general database table or one organized by companies. None of these choices are particularly convenient, since they truncate long names, making contacts harder to find visually unless you adjust the sizes address card by card. By using a separate pane as a table of contents, Kontact sidesteps this problem.

KMail Contacts
Individual entries in Evolution and Kontact are similarly tabbed collections of data. Evolution scores points by automatically inverting names so the last name is first, something you can do in Kontact, but not automatically. But, in general, the contents are both richer and more economically arranged in Kontact. Kontact uses a single tab for email, phone, and mailing address where Evolution uses two, and also adds separate tabs for personalized encryption settings, photos and geolocation, and custom fields, giving it a diversity that Evolution's contact settings lack.

Evolution Contacts
However, where KMail really excels is in distribution lists. Although you are supposed to be able to create a contact list by dragging and dropping in Evolution's address books, I have yet to manage the task in either Debian or Fedora, my main desktop distributions. Yet, in KMail, distribution list controls are place directly below the table of contents, making them easy to organize and find. What is more, the controls work.
Verdict: KMail. Evolution's contacts are clumsy in comparison.
One aspect of Evolution that has always bothered me is that To and CC entries are confined to a single field apiece, making viewing a complete list of either difficult at times. You also have to enter the View memory to add a BCC field. To my relief, KMail solves both problems with a combo box beneath the default fields.
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