Phishing Protection

## Prerequisites
- [x] I have searched open and closed issues for duplicates.

## Feature
**Is your feature request related to a problem? Please describe.**
Phishing is a real problem. And a few thoughtless clicks can have really unpleasant consequences not only for everyday users. Besides the possibility to use two-factor authentication in mail, the client should try to protect its users in the best possible way.

**Describe the solution you'd like**
It would be conceivable for Mail to show its users visually, for example by using (warning) symbols or markers, if the sender addresses differ from the domain and header. It would also be conceivable if Mail could show me the positive. So if domain and header sender addresses are consistent.

**Existing work**
Tutanota already supports this. Unfortunately the solution is not so well documented in the user manual https://tutanota.com/howto/#login (at the bottom).

**EDIT** Exciting, Tutanota has published an extra block article on this topic today. Perhaps there are even more good ideas in it to protect Mail users in the future.
https://tutanota.com/blog/posts/how-to-prevent-phishing/
For example, I like the idea that supposedly malicious and fake mails are moved directly into the SPAM folder.

**EDIT2** The people at Tutanota have continued to work on their phishing protection. Maybe some of these measures can be integrated well into Mail as well. https://tutanota.com/blog/posts/release-email-phishing-protection/

**Additional context**
In the Geary issue tracker there is a collection of ideas for further improvements. Maybe exciting for Mail as well? https://gitlab.gnome.org/GNOME/geary/issues/159