fix: add exception handle on problematic SMTP config

[LeslieLeung]

As mentioned in #39 , a problematic SMTP config might cause a unhandled exception. Trying to add a global Exception to solve the problem and provide a clear error message which should look like:

ERROR:heimdallr.channel.email:Email send failed: [Errno 8] nodename nor servname provided, or not known

The global Exception thingy is not recommended I guess, hope I'll come around and fix this later.

[sonarcloud[bot]]

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