don't share the auth handler for all smtp transport
bug #70 don't share the auth handler for all smtp transport (tecbot)

This PR was squashed before being merged into the 2.2-dev branch (closes #70).

Discussion
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don't share the auth handler for all smtp transport

Currently it's not possible to use different auth parameters for multiple smtp transports because the auth handler is shared.

Commits
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86fb0c3 don't share the auth handler for all smtp transport