Default content-type header

[TylerPachal]

Changes proposed in this pull request

If an email (or a part of a multipart email) has no content-type header, a default of Content-Type: text/plain; charset=us-ascii is assumed.

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This is not part of the RFC 2822 but is part of RFC 1341:

If no Content-Type is specified, either by error or by an older user agent, this default is assumed

[bcardarella]

Does RFC 2822 reference 1341 in any way? I cannot find one.

[TylerPachal]

I am not sure - at least not directly. This came about because I essentially have a wrapper module around elixir-mail that does this same functionality because everything downstream in my application expects a Content-Type.

I suppose that if we are sticking to a strict implementation of RFC 2822 then this can be closed.

This is kind of related to our conversation in https://github.com/DockYard/elixir-mail/issues/83 where we talked about having a more lenient parser because of all of the bad email out there.

[bcardarella]

I think there could/should be a more lenient parser but it doesn't need to be RFC 2822 parser, it can borrow from it though. It could be something like CommonParser that is more true to real-world implementations.

[bcardarella]

Closing per my comment https://github.com/DockYard/elixir-mail/pull/116#issuecomment-625240613