email not being deleted

[Matt]

I assume you are using IMAP and not POP3.

In my Thunderbird I have it set like this:

Tools > Account Options > (some account here) > Server Settings > When I delete a message "Move it to the trash folder" and it goes to the trash immediately without having to delete and then purge.

You might try that option as it saves a step with the whole strikethrough thing. If that doesn't work for you then it may be a bug in your thunderbird version.