Rated 1 out of 5 stars

Sorry 2 say, but it is horrible slow. Using dovecot on OpenBSD to manage my EMails (imap) I have to wait several sends for every click in Thunderbird.

This review is for a previous version of the add-on (5.1.1). 

To improve the speed I would suggest to try the following:
- Enable reading of the Authentication-Results header
- Enabling caching of the DKIM keys

If that does not help please open an issue (https://github.com/lieser/dkim_verifier/issues) so the cause can be investigated further.