I tried to find a way to create a link in a tiddler in my wiki that would refer to a specified email in Thunderbird, but I couldn’t find a solution. One attempt was to use the message-id of the email with a mailto:, but apparently mailto: is used to create new emails and not to link to existing ones.
Another solution had me enable javascript.allow.mailnews in Thunderbird, but I don’t have such an option. Anyway according to what I read there may be security risks in allowing this option in Thunderbird.
A solution to save the relevant emails as .eml files and then link to them in my wiki is not really an efficient way to do it although it produces a result.