We had this error in our neo4j pod recently:
```
2019-12-02 08:29:42.680+0000 ERROR Unable to schedule bolt session 'bolt-1018230' for execution since there are no available threads to serve it at the moment. You can retry at a later time or consider increasing max thread pool size for bolt connector(s).
2019-12-02 08:29:42.680+0000 ERROR Unable to schedule bolt session 'bolt-1018224' for execution since there are no available threads to serve it at the moment. You can retry at a later time or consider increasing max thread pool size for bolt connector(s).
2019-12-02 08:29:42.681+0000 ERROR Unable to schedule bolt session 'bolt-1018352' for execution since there are no available threads to serve it at the moment. You can retry at a later time or consider increasing max thread pool size for bolt connector(s).
2019-12-02 08:29:42.682+0000 ERROR Unable to schedule bolt session 'bolt-1018243' for execution since there are no available threads to serve it at the moment. You can retry at a later time or consider increasing max thread pool size for bolt connector(s).
```
Apparently the default is 400 threads. So we must have a leak somewhere.
* If the email middleware does not send mails, it will give a warning
similar to sentry middleware
* Eliminated GrapphQLClient in one more test
* Rename code => nonce
Sending a mail with further instructions even if the email is invalid
seems to be a good practice: A potential attacker will not now if a user
has an account under that email address. If a user does not remember the
email address, but has control over the other mail account, she will get
feedback that this mail account is incorrect.
