Which virus types can be transmitted via email?

I agree that it's not a boot record virus. Boot sector virus exists on the host and propagate by attaching themselves to executable. It's not worms because worms propagate through network connections. It's Exec file and Trojan. Trojan is an executable that seems benign but carry the viral payload. The two are common executable.

Worms
2. Trojan horse

Usually email attachments are documents, pictures or zip files. EXE files are usually too large to be sent as mail attachments hence EXE file virus is not appropriate. Boot record virus is deposited into a system through floppy media and not via email.