Integration of Norton Anti-Spam with eMClient

Outlook offers an integrated tab for Norton AV allowing users to mark an email as spam or not spam.

Even more important, after marking an email as spam (which then auto-moves it to a spam folder), they also offer an option to send the email to Norton for review and to improve their spam filtering and that seems to quickly stem the flow of similar offers.

(There is also a sub-option to also immediately block that sender - which I never used as the sender always seemed to be a one-off spoofed address).

Norton anti-spam integrates in outlook, according to me, only with mail to pop and not imap

eM Client already offers these options, independent of the anti-virus application you are using.

If there is an email you want to mark as spam, right-click on the message and choose Move to Junk > Move to Junk and Blacklist sender/domain. Thereafter, regardless of what anti-virus application or email provider you are using, messages from that sender/domain will automatically be moved to Junk.

when setting the appropriate filtering rules,
the email client should be able not only to move the message to the trash,
but also to delete it from the server

If you look in the Rule dialogue, there is an option to permanently delete the message.