Fix email: use send_message, set timeout

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (56fbf0d) 95.78% compared to head (80a553f) 95.78%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #209 +/- ## ======================================= Coverage 95.78% 95.78% ======================================= Files 42 42 Lines 2707 2707 Branches 339 339 ======================================= Hits 2593 2593 Misses 90 90 Partials 24 24 ``` | [Files Changed](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/209?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer) | Coverage Δ | | |---|---|---| | [bemserver\_core/email.py](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/209?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer#diff-YmVtc2VydmVyX2NvcmUvZW1haWwucHk=) | `100.00% <100.00%> (ø)` | |

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