Make DKIM canonicalization configurable
I've been encountering some DKIM validation errors with my outgoing mail recently. It turns out that the simple canonicalization algorithm is not very robust and breaks easily, and it usually better to use relaxed instead unless there is a good reason not to:
https://wordtothewise.com/2016/12/dkim-canonicalization-or-why-microsoft-breaks-your-mail/
This PR makes DKIM canonicalization configurable for users. The default is still The default is now relaxed/simple as it was before to avoid breaking things. Perhaps it would make sense to use relaxed/relaxed by default, what do you think?relaxed/relaxed which I feel like is what most users would want.
Edited by Ero Sennin